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Sustainability 2021, 13, 13938. https://doi.org/10.3390/su132413938 www.mdpi.com/journal/sustainability

Review

A Critical Assessment on Functional Attributes and

Degradation Mechanism of Membrane Electrode Assembly

Components in Direct Methanol Fuel Cells

Arunkumar Jayakumar 1,*, Dinesh Kumar Madheswaran 1 and Nallapaneni Manoj Kumar 2,*

1 Green Vehicle Technology Research Centre, Department of Automobile Engineering, SRM Institute of

Science and Technology, Kattankulathur 603203, India; [email protected] 2 School of Energy and Environment, City University of Hong Kong, Kowloon, Hong Kong

* Correspondence: [email protected] (A.J.); [email protected] (N.M.K.)

Abstract: Direct methanol fuel cells (DMFC) are typically a subset of polymer electrolyte membrane

fuel cells (PEMFC) that possess benefits such as fuel flexibility, reduction in plant balance, and be‐

nign operation. Due to their benefits, DMFCs could play a substantial role in the future, specifically

in replacing Li‐ion batteries for portable and military applications. However, the critical concern

with DMFCs is the degradation and inadequate reliability that affect the overall value chain and can

potentially impede the commercialization of DMFCs. As a consequence, a reliability assessment can

provide more insight into a DMFC component’s attributes. The membrane electrode assembly

(MEA) is the integral component of the DMFC stack. A comprehensive understanding of its func‐

tional attributes and degradation mechanism plays a significant role in its commercialization. The

methanol crossover through the membrane, carbon monoxide poisoning, high anode polarization

by methanol oxidation, and operating parameters such as temperature, humidity, and others are

significant contributions to MEA degradation. In addition, inadequate reliability of the MEA im‐

pacts the failure mechanism of DMFC, resulting in poor efficiency. Consequently, this paper pro‐

vides a comprehensive assessment of several factors leading to the MEA degradation mechanism

in order to develop a holistic understanding.

Keywords: direct methanol fuel cells (DMFCs); polymer electrolyte membrane fuel cells (PEMFCs);

membrane electrode assembly (MEA); methanol crossover; polarization; methanol oxidation; flood‐

ing; Nafion®; platinum (Pt); ruthenium (Ru)

1. Introduction

Accelerated climate change and environmental degradation are being suffered glob‐

ally due to the widespread use of fossil fuels [1]. Fuel cells fall under the category of po‐

tential reliable energy systems [2], as most of the renewable energy systems suffer due to

their intermittent operational nature [3]. Amongst different types of fuel cells, polymer

electrolyte membrane fuel cells (PEMFCs) are arguably the fastest‐growing and most

likely to be used in the near future because of their unique attributes such as high power

density, low operating temperature (60–80 °C), quick start‐up, and dynamic response [4].

In particular, when compared to redox flow batteries [5] and Li‐ion batteries [6], PEMFC

is deemed to be a superior candidate considering numerous factors such as capital cost,

electrical efficiency, dynamic response, and power density. Incidentally, the widely used

fuel for PEM fuel cells is hydrogen, which poses challenges and concerns in terms of stor‐

age and safety that subsequently impede its widespread commercialization [7]. Therefore,

significant endeavors have been committed to incorporate direct alcohol fuel cells

(DAFC), considering its distinctive benefits such as simple operation, capability, high en‐

ergy density, safe fuel handling and reasonably low environmental impact. Additionally,

Citation: Jayakumar, A.;

Madheswaran, D.K.; Kumar, N.M. A

Critical Assessment on Functional

Attributes and Degradation

Mechanism of Membrane Electrode

Assembly Components in Direct

Methanol Fuel Cells. Sustainability

2021, 13, 13938. https://doi.org/

10.3390/su132413938

Academic Editor: Nicu Bizon

Received: 15 November 2021

Accepted: 15 December 2021

Published: 16 December 2021

Publisher’s Note: MDPI stays neu‐

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Copyright: © 2021 by the authors. Li‐

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This article is an open access article

distributed under the terms and con‐

ditions of the Creative Commons At‐

tribution (CC BY) license (http://crea‐

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Sustainability 2021, 13, 13938 2 of 28

DAFC was established to tackle the storage crisis of hydrogen as well as to avoid the ne‐

cessity of a reformer for the conversion of alcohol to hydrogen [8].

DAFC that uses methanol as a fuel is normally referred to as direct methanol fuel

cells (DMFC). Methanol is the extensively utilized fuel for DAFC applications and on a

volumetric basis, it has 50% higher specific energy density (6.09 kWh kg−1) than liquid

hydrogen (3.08 kWh kg−1), and it is simple alcohol, with only one carbon atom, which

oxidizes more effectively than other liquid hydrocarbon fuels. In addition, the methanol

infrastructure is well established and safer, unlike hydrogen. [9]. Low boiling point (65

°C), high flammability, and ability to flow through the membrane from the anode to the

cathode side (i.e., high crossover) are the limitations of using methanol as a fuel for

DAFCs, because the chemical oxidation of methanol and the fuel crossover throughout

DMFC operation culminates in a reduced power output, which substantially limits the

widespread usage of DMFCs. Additionally, the methanol feed is diluted with CO2 and

probably nitrogen, which may comprise CO traces that act as a catalyst poison [10]. CO

could be removed from fuel feed using water gas shift and oxidation reactors; however,

the removal adversely affects the system efficiency and leads to an increase in volume,

weight, start‐up period, and response to variations in energy demand of the system [9,11].

Ethanol, on the other hand, can be used as an alternative fuel because of its advantages

such as higher energy density than methanol, and its relatively low toxicity. Ethanol pos‐

sesses additional benefits such as lower cross‐over rates that have less detrimental impacts

on DAFCs performance; however, ethanol has two carbon atoms (C‐C) bonded, and this

bond is quite complex to break at the lower operating temperatures of DAFCs [12]. Eth‐

ylene glycol is an alternative alcohol fuel for DAFCs, which is less toxic, safer in terms of

handling, and has high energy density and lower volatility because of its high boiling

point (about 198 °C) compared to methanol. Moreover, ethylene glycol has a theoretical

energy density of 4.8 Ah mL−1, which is 17% greater than that of methanol, i.e., 4 Ah mL−1,

which is particularly noteworthy for portable electronic applications [13]. Although vari‐

ous types of alcohol are employed as fuel for DAFC, the Direct Methanol Fuel Cells

(DMFC) exhibit higher performance and lower crossover compared to DEFCs. This is be‐

cause, when using ethanol as a fuel, there is a rapid decline in cell voltage at higher current

densities, due to the rapid anode poisoning [14]. Owing to the aforementioned unique

advantages, it is evident why DMFCs are the most widely employed alcohol‐based fuel

cells.

From the structural configuration, the DMFC comprises an anode/cathode gas diffu‐

sion layer (GDL), anode/cathode catalyst layers (CL), and an electrolyte (i.e., a proton con‐

ducting membrane), and bipolar plates (BPPs) on either side. Frequently, these compo‐

nents are engineered separately and pressed all together as a single unit at high pressure

and temperature. The CL and GDL integrated with the membrane, as a single unit is re‐

ferred to as membrane electrode assembly (MEA). This DMFCs’ configuration is similar

to that of a PEMFC stack. Methanol with water is fed through the flow channels of BPPs

on the anode side of the cell through the flow channel of the bipolar plates and oxygen is

fed on the cathode side.

The methanol and water react electrochemically and generate protons, electrons, and

CO2 at the anode, due to the methanol oxidation at the CL, as given in Equation (1). The

membrane (Nafion®) conducts protons to the cathode and impede the electrons since the

membrane is ionically conductive. The membrane also aids in CO2 rejection, because in‐

soluble carbonates are produced in alkaline electrolytes. The electrons thus travel through

an external circuit, producing electrical energy and recombining with protons on the cath‐

ode side with oxygen atoms and producing water, as given in Equation (2). The overall

reactant flow and the ion transfer mechanism is depicted in Figure 1 and given in Equation

(3) [15–18].


Figure 1. Schematic of DAFC and the Ion transfer Mechanism.

Anode reaction: 𝐶𝐻 𝑂𝐻 𝐻 𝑂 → 𝐶𝑂 6𝐻 6𝑒 𝐸° 0.046 𝑉 (1)

Cathode reaction: 𝑂 6𝐻 6𝑒 → 3𝐻 𝑂 𝐸° 1.23 𝑉 (2)

Overall reaction: 𝐶𝐻 𝑂𝐻 𝑂 𝐻 𝑂 → 𝐶𝑂 3𝐻 𝑂 𝐸 1.18 𝑉 (3)

The most broadly employed membrane for DMFCs is Nafion®, as it demonstrates

exceptional proton conductivity, as well as outstanding mechanical and chemical stability.

However, Nafion® possess high fuel crossovers throughout the membrane and they are

costly, have inadequate device lifespans, owing to the chemical and mechanical degrada‐

tion. Hence, the potential constraint of the DMFC system is that it deteriorates from des‐

titute anode kinetics, high catalyst loadings, low power density, and high cost [19–21].

Thus, DMFC and DEFC belong to the same family with marginally different characteris‐

tics.

In general, methanol should oxidize readily when the anode potential exceeds 0.046

V in proportion to the reversible hydrogen electrode (RHE). Correspondingly, when the

cathode potential falls under 1.23 V, oxygen should be decreased gradually. In practice,

the sluggish electrode kinetics (kinetic losses) drive electrode reactions to vary from their

ideal thermodynamic values, resulting in a substantial reduction of the theoretical cell

efficiency [22]. For any fuel cells, the performance, a good grade of stability is a vital re‐

quirement and subsequently, the degradation mechanisms for DMFC components have a

direct influence on the performance of DMFCs [23]. In addition, the operating circum‐

stances and the degradation processes are directly co‐related, given that the degradation

of active‐type DMFC performance during cyclic voltage loading is significantly greater

than under continuous voltage or current operation [24]. However, minimal consideration

has been committed to studying the degradation mechanism of the membrane electrode

assembly of DMFCs. The present paper provides prominence to the general MEA degra‐

dation mechanism of the DMFC system. Considering all these aspects, the paper is cate‐

gorized into the following sections: Section 2 elaborates on the functional attributes of the

various DAFC stack components including the membrane, CL, and the GDL. Section 3

expounds on the degradation involved in the MEA. Section 4 exemplifies the degradation

mechanism in the DMFC component arranged systematically. Section 5 summarizes the

significance of the work along with the critical assessment and limitations.

2. DMFC Functional Components

The critical components of the DMFC are the membrane electrode assembly which

encompasses the membrane, CL and GDL. To be empathetic on the root causes in the


MEA degradation involves the understanding of its functional attributes which are elab‐

orated in the subsequent section.

2.1. Membrane

The membrane acts as a separating layer between the anode and cathode layer, which

conducts protons and impedes the flow of electron. The membrane ought to have high

proton conductivity, high chemical stability, and must be minimally permeable to meth‐

anol and water while possessing high durability at a reasonable cost [25,26]. The mem‐

branes for DMFC are normally based on fluorinated polymer and sulfonic acid groups

similar to the PEMFC systems [27]. Nafion® is the widely used membrane, which is a per‐

fluorinated polymer, primarily composed of a polytetrafluoroethylene (PTFE) support

and lengthy perfluoro vinyl ether pendant side chains that are wrapped up by sulfonic

functional groups. The polytetrafluoroethylene (PTFE) support offers chemical and ther‐

mal conductivity, while the sulfonated group ensures proton conductivity. The membrane

is normally 175 microns in thickness, and the electrodes are typically 2 mm in thickness

[28]. Many commercially available membranes are below 175 microns in thickness, but

they are not reported to be efficient in proton conduction in the DMFC [29]. The chemical

structure of a Nafion® perfluorinated ionomer is given in Figure 2 [30].

Figure 2. Typical structure of Nafion® perfluorinated ionomer [30].

The X in the structure of Nafion® predominantly refers to the sulfonic ionic functional

groups and the M refers to the metal cation in neutral form of a proton (H+) in the acidic

form. Typically, a perfluoro sulfonyl fluoride copolymer‐based Nafion® from DuPont,

Delaware, USA is observed as the best‐fit membrane for DMFCs, due to its high proton

conductivity, exceptional mechanical properties, excellent chemical stability, and easy

availability. However, it has shortcomings such as high manufacture expense, and at low

humidity or high temperatures, these membranes are less proton conductive, have low

mechanical property, high alcohol permeability, and are limited to operating tempera‐

tures [31]. As a result, such Nafion® membranes are susceptible to rapid dehydration at

high temperatures, resulting in loss of proton conductivity, and in certain circumstances,

causes irreversible changes in the microstructure of the membrane [32]. As a consequence,

the key difficulties in contemporary DMFC research are to produce an alternate mem‐

brane capable of operating at higher temperatures or with low humidification of reactants.

Choices of Nafion®, on the other hand, are frequently cheaper, i.e., sulfonated polyether

ether ketone (sPEEK) membranes [33] and sulfonated poly aryl ethers (SPAEs) [34]. Few

commercially available membranes for DMFCs are Aciplex (Asahi Kasei Chemicals, To‐

kyo, Japan) [35], Flemion (Asahi Glass, Chiba, Japan) [36], Gore‐select (W. L. Gore & asso‐

ciates, Delaware, USA) [37] and the perfluoro sulfonic acid (PFSA) based Fumapen F‐1850

and E‐730, (Fumatech Bietigheim‐Bissingen, Germany), [38] though Nafion from Dupont

is the most prevalent.


2.2. Gas Diffusion Electrode (GDE)

The GDL and the electrode (catalyst) as a single unit is referred to as gas diffusion electrode (GDE) [39]. The GDE for DMFC is typically made of a porous mixture of carbon‐

backed platinum (Pt) or Ruthenium (Ru) [40]. Pt is predominantly used as the electrocat‐

alyst for DMFC. However, with methanol as a fuel, there could be “CO poisoning.” There‐

fore, Ru is added to promote the electrocatalyst activity by adsorption of OH and strip‐

ping off adsorbed CO from nearby Pt sites. Thus, at the anode, the catalyst, namely, Pt/Ru,

in appropriate proportion initiates the methanol electro‐oxidation to generate protons and

electrons [41]. For an effective electrochemical reaction, the catalyst particles should be in

close proximity with the protonic and electronic conductors. Additionally, there should

be sections for reactants (i.e., porosity) to reach the catalyst zone and for reaction products

to leave the cell [42]. The contact point of reactants, catalyst, and the electrolyte is usually

indicated as the three‐phase interface [43]. To accomplish an adequate rate of reaction, the

area of catalyst zones must be several times greater than the geometrical area of the cata‐

lyst. Consequently, the catalysts are made porous to form a three‐dimensional network,

where the three‐phase interfaces are established [44]. The catalysts are typically 0.45 mm

thick (before hot‐pressing), with a catalyst loading that lies within the range of 0.2 to 0.5

mg/cm2. The catalyst loading is one of the cost‐hindering aspects of the DMFC, compared

to other MEA components, given that Pt‐Ru/C anode catalyst constitutes 36% and Pt/C

cathode catalyst constitute 21% of the overall cost of a single DMFC stack in mass produc‐

tion (10,000 units per year), while the membrane and GDL const 12% and 8%, respectively

[45]. The DMFC stack cost could not be downsized unless the amount of Pt is reduced by

any cost‐effective element combined with it, or by entirely replacing Pt with any non‐

noble elements. Alternative catalysts can be investigated in addition to lessening the CO

contamination, thereby reducing the overall cost of the DMFC [46]. Though in certain cir‐

cumstances, the catalysts are coated onto the membrane, as in the present context, it is

taken into the account the CL and GDL as the gas diffusion electrode. The precious cata‐

lyst is typically Pt, which has the highest activity towards oxygen reduction reaction

(ORR) compared to all catalysts grounded on the Sabatier principle. This systematic con‐

figuration is termed as volcano plot and is illustrated in Figure 3 [47].

Figure 3. Volcano plots showing the catalytic activity trends as a function of the binding energy [47].

The GDL in general comprises a macroporous backing layer, usually made of porous,

conductive carbon cloth or carbon cloth, and a microporous layer (MPL) [48]. Good diffu‐

sion characteristics (facilitating reactants to come in contact with the catalyst site); good

electrical conductivity; stability in the DMFC environment; high permeability/pore size

distribution for liquids and gases; good elasticity under compression; contact angle of the

pores are the favorable features of GDE [49]. The most widely available carbon cloth‐based

GDL are ELAT [50], Avcarb [51] and CeTech [52], where carbon paper‐based GDL are


Avcarb [53], Toray [54], Freudenberg [55], Sigracet [56] and Spectracarb [57]. Carbon cloth

has an ordered arrangement of fibers, larger pores, high porosity, and permeability, re‐

sulting in reduced mass transportation resistance and accelerating effective CO2 removal

[58]. Carbon paper, on the other hand, has a packed high denser structure and could be

utilized to improve back diffusion of water by retaining a hydraulic pressure at the cath‐

ode [59]. A study on structural multiplicity and acclimatization dependence of DMFC re‐

ported that, using carbon cloth as the anode GDL and carbon paper as cathode GDL for a

DMFC outperformed all other configurations [60]. Metal foams, metal meshes, and sin‐

tered metals are used as alternative GDLs in DMFCs [61,62]. Studies reported that the

metal foam‐enhanced passive DMFC performed better in terms of oxygen transportation

and consequently cell performance [63].

3. MEA Degradation and Mitigation Strategies in DMFC

The MEA has often been termed the heart of DMFC. An insight into the degradation

mechanism of the MEA can apparently increase the reliability of the DMFC stack. As a

consequence, an assessment of the degradation in the membrane and gas diffusion elec‐

trode of a DMFC stack is mandatory. A comprehensive and systematic review is a prom‐

ising way of representing such degradation, as those events can be classified as the pri‐

mary, secondary, and tertiary consequences which cause the degradation of the stack

components. This article logically assesses the combinations of the undesired events that

can potentially lead to the undesired state based on numerous research articles reported.

The primary consequences are those unsought or most intricate causes, the secondary

consequence is the intermediate cause, and the tertiary consequences are at the bottom. In

the present work, an assessment is performed on those degradation mechanisms that can

lead to the failure of MEA components of DMFC. Nevertheless, similar assessments have

been already performed by several researchers that largely focus on hydrogen‐based

PEMFCs [64–67]. Though the degradation of DMFC is similar to hydrogen‐based PEM‐

FCs, there are significant alterations that have to be assessed. The following sections elab‐

orate on the degradation mechanism in the MEA components of DMFC.

3.1. Electrolyte Membrane

The primary constituent of the membrane degradation is the methanol crossover, fol‐

lowed by various other constituents such as CO poisoning, membrane thickness, metha‐

nol concentration, and its impurities, membrane assembly defects, reaction parameters,

thermal and mechanical stability, and radical (OH*/HOO*/ROO*).

3.1.1. Methanol Crossover

In a liquid‐fed DMFC, methanol in excess is provided to the anode of the MEA. It is

desired to have all or for most of the methanol diffuse into the anode for the reaction. A

phenomenon follows called “methanol crossover (MCO)” where a certain amount of the

methanol diffuses over the membrane from the anode to the cathode [68]. The MCO in

general is defined using Fick’s law for diffusion across a polymer membrane as given in

Equation (4) [69] and its schematic representation is given in Figure 4 [70].

𝐽 𝐷𝑑𝐶𝑑𝑍 (4)

where J is the methanol flux, D is the coefficient of diffusion, C is the methanol concentra‐

tion and Z is the location within the membrane.


Figure 4. Schematic representation of methanol crossover in DMFC [70].

The Inherent water diffusion characteristic of the membrane and methanol solubility

in water triggers MCO [71]. Consequently, merely a few elements of methanol oxidize at

the anode layer, where the rest of the elements are diffused through the membrane result‐

ing in MCO [72]. This transportation is primarily by the diffusion and electro‐osmotic drag

(EOD) mechanism [73]. The mass transportation diffusion mechanism is fundamental

during MCO, and it is proportional to methanol feed concentration. EOD is generated

when proton transfer drags several methanol molecules. The EOD contribution is propor‐

tional in MCO., i.e., it increases with increase in amount of methanol fraction at the mem‐

brane‐electrode (anode) interface and the current generated by the cell [71].

The MCO occurs mostly owing to the nature of the Nafion membrane, as Nafion is

made up of hydrophilic side chains that comprise ionic sulfonic acid (–SO3H) groups,

which clustered in conjunction to produce ionic channels. While the water flow through

ionic channels aids in the transport of protons, allowing for superior proton conductivity,

it allows for the passage of methanol across the membrane. This aliphatic polymer struc‐

ture of Nafion facilitates the development of larger ionic channels, resulting in enhanced

methanol permeability [72].

Studies reported that the MCO mostly relies on the operating temperature [74–76]

and the method of delivering the fuel [77]. It is given that the rate of fuel/oxidant deliv‐

ered, and their concentration will substantially impact MCO [78]. The linear dependency

of current density on temperature and methanol concentration was reported in numerous

studies [79–83]. Figure 5 [84] represents cell current density versus methanol crossover

current density as a function of temperature and methanol concentration, respectively.

While the precise co‐relation between permeability and MCO is complicated, certain var‐

iables such as the thickness of membrane [85] and methanol feed concentration [86] im‐

pact crossover in definite directions, i.e., for greater methanol concentration or thinner

membrane, the crossover rates are higher [87]. In addition to permeability, the co‐efficient

of diffusion and solubility properties are often reported [88]. It is essential to measure

these concepts and connect them to the MCO fluxes of operational DMFCs at this phase.

This MCO leads to lower theoretical open‐circuit voltage (OCV) of ~0.7 to 0.8 V vs. ~1.2 V

and low power density of DMFC [89]. MCO produces a mixed potential at the cathode,

and consequently decreases the methanol consumption in the anode, thereby decreasing

the voltage of the DMFC around 400 mV [90].

The most amount of the MCO to the cathode will be electrochemically oxidized. This

leads to the decrease in the performance of the cell and is subjected to the consumption of

the cathode reactants [91]. In prevailing liquid feed DMFC, dilute methanol (6.41% to 9.61

vol% CH3OH or 2 to 3 mol) is provided to the anode side of MEA. In such instances, the

methanol diffuses to the anode and reacts incompletely.


Figure 5. Cell current density versus methanol crossover current density as a function of tempera‐

ture a methanol concentration [84].

The residual methanol leaves the CL and thus diffuses through the membrane to the

cathode. The deficit of fuel decreases efficiency, which consequently reduces the cathode

performance. The methanol loss at the anode side initiates the concentration at the surface

of the catalyst to deterioration in the vicinity of the membrane accelerates the mass trans‐

portation resistance [92,93].

The hydrophilic properties of Nafion are enhanced by the concentration of hydro‐

philic domains and as a result, DMFCs elements are easily transported over perfluoro

sulfonic acid membranes (mostly water and methanol). This consequently influences

MCO from the anode to the cathode, which is primarily accomplished by the diffusion via

the water‐filled channels inside the Nafion structure and active transportation with pro‐

tons and associated water solvent molecules during EOD [94]. A rigid polymer matrix [95]

and a small free‐volume membrane [96] could potentially bring down the electro‐osmosis

methanol diffusion. At the cathode, the MCO is oxidized to CO2 and H2O, lowering fuel

efficiency and leading to cathode depolarization [97]. It is postulated that MCO reduces

the efficiency of DMFC by 35%. Although the loss of oxygen from the cathode to the anode

has an adverse effect on the efficiency of DMFC, it may be overlooked in contrast to the

impact of the MCO. On contrary, mass transfer of N and CO through the membrane has

no substantial effect on DMFC performance [95].

It is evident from studies that the MCO is a significant factor that leads to the degra‐

dation of the membrane component. From the findings of various experiments reported,

higher methanol concentration and substantial membrane thinning was detected, because


the Nafion is soluble in methanol. This results in increased MCO and intense mixed po‐

tential formation on the cathode. Thus, the incompetence of the membrane to function as

an efficient alcohol barrier decreases the performance of the cell as a result of mixed po‐

tential at the cathode [98–101]. Figure 6 [102] illustrates a graph comparing methanol

crossover rates at OCV condition and in the presence of 1 and 5 M methanol concentration

for some of the tested membranes including the commercial Nafion® 115. This measure‐

ment was performed by employing an online gas chromatograph to analyze the CO2 at

the cathode. In the sequences E‐730, F‐1850, and Nafion®‐115, the crossover increased.

Figure 6. Methanol crossover rate of different membranes under different operating conditions

(temperature and methanol concentration) [102].

Numerous studies have examined DMFC performance utilizing anion exchange

membranes (AEMs) rather than the more typical proton‐based Nafion membrane, with

the vast majority reporting higher Ohmic resistance and lower MCO [103–105]. While

AEM‐DMFCs have a greater OCV and marginally improved initial performance com‐

pared to Nafion‐based DMFCs, the resilience of such membranes often degrades in con‐

trast to Nafion‐based membranes, culminating in quick performance degradation [106–

108]. The quaternized polyaromatics‐based AEM polymers such as quaternized polyether

ketone and quaternized polysulfone have recently received considerable attention, be‐

cause of their outstanding conductivity properties, good mechanical and chemical stabil‐

ity [109,110]. However, synthesis of quaternized polyaromatics embraces hazardous com‐

pounds such as chloromethylation of benzene rings, which are highly carcinogenic and

cytotoxic. Furthermore, the cost for tailoring polymers of quaternized polyaromatics is

relatively expensive, which stands as the primary impediment to widespread commer‐

cialization [111,112]. Table 1 [113] provides the snapshot of electrochemical characteristics

of different membranes used for DMFC.

Table 1. Electrochemical characteristics of different membranes used for DMFC [113].

Membrane Acronym E‐730 F‐1850 Nafion 115 Type of polymer SPEEK PFSA PFSA

Equivalent weight (g mol−1) 700 1800 1100

Membrane thickness (μm) 30 120 125

Crossover current (mA cm−2) 48 100 195

Maximum power density @

90 °C (mW cm−2) 77 38 64

Various studies have been conducted to control MCO [114,115]. The methanol con‐

centration gradient through the Nafion membrane has high impacts over MCO; however,

this approach is said to increase flooding and result in lower energy density [116]. Given


that, the methanol tolerant catalysts cannot directly control the MCO rate, though it is

capable of reducing the detrimental consequences of it [117–119].

3.1.2. Stack Assembly Effects

At high operating temperatures, the membrane degradation rate accelerates owing

to the development of pinholes in the membrane in conjunction with cathode degradation

and delamination [120]. If any flaw or pinhole appears on the membrane, the reactants

blend under the catalytic effect that forms reaction intermediates such as CO, resulting in

the hot‐spot formation and, in turn, the pinhole dimensions or structural deformation

[121]. In extreme circumstances, this could contribute to the explosion of cells, or struc‐

tural flaws are caused by the following reasons: (i) When the membrane is stabbed by

fibers or particles in the MEA during manufacturing and processor during stack assembly

[122]; (ii) When the membrane is stabbed or lacerated by MEA or bipolar plate edges un‐

der stress produced by the stack bolts [123]; (iii) During long‐term operation of the stack,

peroxide corrosion makes the membrane thinner, and which leads to pinhole formation,

that are more likely to be appeared in membrane drying cases [124]. Despite the above‐

mentioned reasons, membrane pinhole development can occur under extremely transient

circumstances with a high number of humidity cycles. Because of the substantial volumet‐

ric expansion of ionomeric membranes under high humidity and in the presence of liquid

water, variations in RH cause high mechanical stresses in the membrane, which contribute

to membrane pinholes through in the lack of chemical degradation [122]. However, the

pinhole formation triggered by short‐term mechanical damage or steady long‐term corro‐

sion is not known as their effects on performance are not apparent; hence, it is imperative

to develop approaches for perceiving membrane pinholes formation to circumvent the

potential hazard of explosion or constant performance reduction, and subsequently the

reduction in lifespan.

Studies have shown that stresses developed within the system could damage the

membrane. These developed stresses are said to have various origins. The first is the initial

stresses that arises within the MEA during stack assembly [125]. Numerous studies on

optimizing the assembly procedure (such as bolt assembly), especially for the homogeni‐

zation of the arising mechanical stresses have been reported [126]. A study on the me‐

chanical response of membrane subjected to various clamping conditions observed the

formation of pinhole at the center of the membrane which is due to the extreme form of

non‐uniformity in this constraint configuration [127]. One study observed that clamping

stress is conducive to the durability and integrity of the membrane that, however, depends

on the design specifications [128]. Evaluating various stack compression methods by con‐

sidering the vibration effects in the clamping systems of the stack can offer better percep‐

tions of optimal stack assembly procedure. Supplementary efforts are yet to be established

to deliver models that combine the physical and electrochemical process concerning as‐

sembling and structural issues viz. stress, displacement (deformation), damage (cracks,

delamination).

3.1.3. Thermal/Mechanical Stability

In general, Nafion membrane is volatile on operating the stack at temperatures range

of above 100 °C. Better cell performance of the cell for Nafion‐based membranes is achiev‐

able with the operating temperature range of 25 °C to 90 °C. Over 90 °C, the current den‐

sity is limited as temperature increased, because of the membrane degradation [129]. In

recent times, significant attention has been paid to Polybenzimidazole (PBI)‐based mem‐

branes because of their high thermal stability, which is attributed to their tolerance when

operating at higher temperatures (i.e., >100 °C) than Nafion membranes. To achieve max‐

imum power output, it is desirable to increase the operating temperature; PBI membranes

are able to endure while operating at temperatures in excess of 100 °C with a vaporized

feed [130].


3.1.4. Methanol Concentration and Impurities

The other factors leading to the damage of the membranes are the impurities present

in the methanol. DMFCs utilizing various types of commercial methanol con numerous

compositions of impurities. The water content in the humidified methane encompasses

cationic impurities namely Na+, Cl− and Mg2+, that possibly contaminates the membrane

surface [131]. The proton loss is more acute with low‐valent cations, which is due to the

decreased affinity of the sulfonic acid groups present in the Nafion membrane [132]. It

was reported that that the MEA substantially degraded with an increase in the corrosion

of austenitic stainless steel by the supply of various metal solution concentrations into the

fuel stream of DMFC [133]. In addition to impurities with the methanol, the concentration

of the fuel adversely affects the MEA performances. Optimum methanol concentration

fall in the range of 1–2 M, which entails water dilution and subsequently far lower energy

density. The higher alcohol concentration worsens the influence of permeated fuel on the

performance of the membrane due to the MCO effect [134]. A study stated that the mem‐

brane becomes highly porous and the degree of membrane swelling is increased when

there is an increase in alcohol concentration [135]. In general, the pure polar solvent has a

greater membrane absorption than the pure non‐polar solvent. When water is blended

with a solvent, fortunately, the degree of swelling is negatively proportionate to the po‐

larity of the solvent [136].

3.1.5. Membrane Thickness

Membrane thickness in a DMFC influences water crossover as well as water manage‐

ment, which thereby causes membrane degradation. A study reported that when the pas‐

sive DMFC is worked with low methanol concentration and with a thicker membrane

shows better performance at low current densities than at high current densities [137]. The

thinnest sPEEK membrane was proven to have good DMFC performance, though also

showing low Faradays efficiency (i.e., high methanol permeation with low Ohmic losses).

On the other hand, the thickest membrane showed superior qualities concerning metha‐

nol permeation [138].

3.1.6. Reactive Oxygen Species

The formation of reactive oxygen species, such as the hydroxyl radical (OH), and

hydroperoxyl/peroxyl radicals (HOO/ROO) can also cause the degradation of the mem‐

brane. Given that, the Nafion membranes are prone to the high absorption of reactive ox‐

ygen species, which leads to a high swelling ratio rate of membranes and fail to properly

hold the contact between membrane and catalyst [139]. In the case of the PFSA membrane,

the formation of reactive oxygen species also opens up the path for methanol permeabil‐

ity, which leads to high MCO [140].

3.1.7. Mitigation Strategies for Membrane Degradation

The contemporary reliance on Nafion membrane use for DMFC is significant due to

its high conductivity and mechanical and chemical stability. The degradation of Nafion

membranes, on the other hand, represents a considerable drawback. Hence, exploring an

alternate membrane or increasing the performance of the Nafion is critical. Numerous

literature has been reported to address the membrane degradation issue. Concerning the

methanol crossover reduction, it can be accomplished by utilizing cross‐linking proce‐

dures or adding up nanosized inorganic fillers within the membrane to improve the tor‐

tuosity path, as well as by fine‐tuning the ion exchange capacity (IEC) [141]. The alterna‐

tive approach contemplates the change of the chemical characteristics of the polymer net‐

work adjoining the ionic groups to modify the degree of dissociation and the degree of

interpenetrated networks [142,143]. These approaches can reduce the level of methanol

permeation permeability while keeping the proton conductivity at suitable levels; how‐

ever, apparently, the cathode is less polarized in the presence of lower methanol


permeation [144]. This corresponds to lower overpotentials for the oxygen reduction re‐

action. This strategy is further assisted by using methanol‐tolerant cathode electro‐cata‐

lysts with high activity for oxygen reduction [145]. FuMA‐Tech created a new class of

fluorinated membranes for use in DMFCs [146], which exhibited ion exchange capacities

of 0.4 and 0.5 meq g−1, that is nominally equated to equivalent weights of 1800 and 2300 g

mol−1, respectively. These results differed greatly from those of conventional PFSA mem‐

branes, such as Nafion® 115, with an equivalent weight of 1100 g mol−1 and an IEC of 0.91

meq g−1. These blend membranes were designed to restrict methanol crossing, while the

cast membrane thickness of 30–50 m enabled minimizing the membrane area resistance

and cost of material as contrasted to Nafion® 115, which has a thickness of 125 m.

A relationship (reciprocal of the product of the area‐specific resistance and the cross‐

over) between DMFC power density and membrane selectivity is reported in a study

[102]. This equation could be used to estimate DMFC performance based on fundamental

membrane parameters in the presence of identical catalyst‐loading, mechanical, and in‐

terfacial features. As explained above, selectivity is connected to intrinsic membrane fea‐

tures. Consequently, determining membrane selectivity does not always necessitate test‐

ing in DMFCs. Conductivity, thickness, and methanol permeation properties may all be

used to calculate selectivity. If the electrode parameters are known, membrane selectivity

can provide an indicator of DMFC performance at low temperatures, according to our

research.

Using reinforced composite membrane is another strategy to improve membrane du‐

rability in DMFCs. The membrane with silane grafted on graphene oxide‐treated mor‐

denite with graphene oxide shows improved durability than conventional Nafion [147].

A thin Nafion membrane comprised of highly surface‐functionalized sulfonated silica‐

coated polyvinylidene fluoride (S‐SiO2@PVDF) nanofiber mat and methanol‐resistant chi‐

tosan. The proposed membrane showed three times greater wet tensile strength (25.2

MPa) and 1.6 times greater elongation (83.5%) than those of the pure Nafion membrane.

More vitally, the improved ionic conductivity, reduced methanol permeability, and ex‐

tremely limited swelling were attained for the composite membrane. These results show

that the production of such a mechanically robust membrane with improved proton con‐

ductivity, and methanol resistance is a great structural design system. Likewise, in theory,

decreasing the molecular weight or increasing the content of silane coupling agent coating

could help enhance the conductivity of nanofibers. Similar studies were reported using

quaternized chitosan reinforced with surface‐functionalized PVDF electrospun nano‐

fibers [148], Polyvinyl alcohol (PVA) reinforced composite membranes [149], poly(styrene

sulfonic acid)‐grafted poly(vinylidene fluoride) reinforced composites [150], Graphene

quantum dot reinforced hyperbranched polyamide membrane [151], to improve the

DMFC membrane durability.

3.2. Electrocatalyst Degradation

The DMFC widespread hindrance is highly influenced by the degradation of the cat‐

alyst layer which is accelerated by the following reasons: Catalyst poisoning; Pt/Ru ag‐

glomeration; Pt/Ru delamination; Pt/Ru dissolution; Ru leaching from Pt/Ru surface; Sur‐

face oxide formation and the membrane dissolution.

3.2.1. Catalytic Poisoning

CO poisoning, the most severe catalyst deactivation proc, is a critical concern, partic‐

ularly in direct methanol fuel cells (DMFCs). Figure 7 [152] schematically illustrates the

CO formation on the surface of the Pt catalyst.


Figure 7. CO formation on the surface of Pt catalyst [152].

The intermediates of methanol electro‐oxidation impede alcohol oxidation and ab‐

sorb CO molecules on the electrocatalyst surface which then leads to poisoning the elec‐

trocatalyst and hinders the electro‐oxidation kinetics [153]. This consequence lead to the

use of alloys. Ruthenium as a potentially promising circumvent the CO poisoning [154].

In addition, transition metal carbides have benefits in terms of poison resistance; for in‐

stance, tungsten carbide (WC) has unique character traits such as high electrical conduc‐

tivity, acid resistance, relatively low cost, and resistance to CO poisoning during methanol

electro‐oxidation [155].

3.2.2. Pt/Ru Agglomeration

The overall growth in particle size during methanol oxidation is described by ag‐

glomeration. The mechanism varies on the particles’ distance and support characteristics.

Given that the specific particles are in the nearby vicinity or linked to each other, thus

producing the larger sized group, the catalyst material diffused and increase together

throughout potential cycling. This further formed as a layer with the membrane and MPL

on either side and degrades on constant operation [156]. The mechanism of Pt agglomer‐

ation at the cathode side of DMFC is given in Figure 8 [157]. Constant advancements in

catalyst ink development have been attained such as decreasing the Pt/Ru loading and

substituting Pt‐black with Pt‐supported carbon black [144]. The carbon support typically

comprises several carbon black particles, namely, Vulcan (20 μm) or Ketjen black (50 μm).

When the particles turn out to be coupled together by fusion bonding in the ink solution,

then the aggregates produce agglomerates by attractive van der Waals forces [158].


Figure 8. Pt agglomeration at cathode catalyst of DMFC [157].

In a study, aggregates of various forms were modelled as particle clusters and dis‐

tributed randomly in space to develop an agglomerate composition of the catalyst layer.

It was observed that when aggregates overlapped, a new spot of agglomeration was ran‐

domly formed [159].

3.2.3. Pt/Ru Dissolution

Conventional Pt‐Ru‐based electrocatalysts are reported to comprehend a substantial

quantity of unalloyed Ru in the form of intermetallic phases or segregated oxides, which

are responsible for the dissolution of Ru under collapsed pseudocapacitive currents [160].

Pt or Ru dissolution from the Pt–Ru anode catalyst by potentials greater than 0.5 V vs.

DHE, observed by migration and accumulation to the cathode can decrease the activity of

both anode and cathode catalysts and a deterioration of cell performance [161]. Figure 9

[162] illustrates the Pt dissolution mechanism in a typical DMFC. In a study, it is reported

that if the Pt/Ru atomic ratio is unchanged or decreased, it also can lead to Ru losses,

relying on the comparative amount of Pt and Ru lost. The standard Pt/Ru atomic ratio of

the Pt‐Ru catalyst is 1:1, hence, a drop in Ru concentration in the catalyst leads to a decline

in MOR. Nevertheless, based on the degree of alloying, the Pt–Ru catalyst’s MOR activity

would increase after Ru loss [163].

Figure 9. Dissolution of Pt from the surface of carbon‐supported catalyst [162].


3.2.4. Pt/Ru Delamination

Due to the low binding energy between the catalyst‐coated membrane and the CLs,

delamination of CLs often occurs throughout repetitive operations. The bonding force

supplied by the direct pressing approach of CCM cannot withstand the swelling of the

membrane during the operation of the DMFC, resulting in delamination [164]. A study

reported that the isotropic membrane swelling (i.e., expansion coefficient difference be‐

tween the CL and membrane) enhances the variance in swelling ratio with catalyst en‐

compasses a Nafion binder, which would most likely increase electrode layer delamina‐

tion [165].

3.2.5. Ru Leaching from Pt/Ru Catalyst

In the absence of Ru near the Pt catalyst, the firmly bonded CO molecule generated

following reactant transfer will degrade the Pt surface. As a result, it is critical to avoid

certain operating circumstances that lead to Ru leaching [166]. Additionally, the Ru

leached from the anode will be deposited on the Nafion membrane, causing membrane

fouling. Finally, the anode’s leached Ru can be deposited at the cathode, lowering the

cathode catalyst’s total oxygen reduction activity. Though the existence of Ru is crucial

for MOR, when the anode potential achieves 0.5 V vs. RHE, the Ru (in oxidized form)

particles would be receptive to leaching [167]. By quantifying the amount of Ru oxide

from various sections of the DMFC, we can ascertain that the potential distribution in the

cell is not uniform even in a single cell arrangement under typical operating circum‐

stances. Because of the comparatively large anodic potentials, this condition may also re‐

sult in preferential Ru leaching from the methanol inflow area [168].

3.2.6. Surface Oxidation Formation and Practical Growth

The high binding energies of both CO and oxygen‐containing species such as surface

oxides or adsorbed OH groups induce the quite often substantiated poisoning of pure

platinum utilized as an anodic catalyst [169]. Intermediate species may also poison the

catalyst and deteriorate the fuel cell performance. For instance, methanol will partially

oxidize to form intermediate species such as formic acid, methyl formate, and formalde‐

hyde [170]. Pt surface oxidation at the cathode is investigated in numerous studies using

the oxide reduction peak of cyclic‐voltammetry measurements, and it is determined that

the electrocatalytic activity for oxygen reduction decreases, which contributes to degrada‐

tion in the catalyst layer [171]. The substantial, oxidized Ru percentage in the anode cata‐

lyst was demonstrated to exert a major influence in the development of particles at the

anode side and was found to be disseminated throughout the cathode in its oxidized form

and, therefore, can have a considerable impact on the oxygen reduction activity (ORR)

[172].

3.2.7. Carbon Corrosion

Carbon black (specifically Vulcan XC‐72) is the most frequently used backing layer

for DMFCs. These are typically made using pyrolyzing hydrocarbons. The high surface

area (∼250 m2 g−1 for Vulcan XC‐72), low cost, and effortless accessibility of carbon black

help decrease the total cost of the cell [173]. While widely used as a catalyst–support, CBs

still endure complications such as (i) the presence of organo‐sulfur impurities [174] and

(ii) deep micropores or recesses which deceits the catalyst nanoparticles making them in‐

accessible to reactants consequently leading to reduced catalytic activity. Under the acidic

environment of a conventional DMFC, thermochemical stability is essential, and its defi‐

ciency results in corrosion of the carbon support and dissolution of the catalyst layer [175].

Carbon black, on the other hand, is mostly made up of planar graphite carbon and amor‐

phous carbon, both of which have a lot of dangling bonds and flaws. The dangling bonds

quickly generate surface oxides, leading to a faster corrosion rate during electrochemical


oxidation [176]. A study reported that agglomeration of catalysts which is triggered by

reactant starvation is correlated to carbon support corrosion [177].

3.2.8. Mitigation Strategies for Catalyst Degradation

Among various degradation mechanisms, the Pt/Ru agglomeration and dissolution

were found to be the most significant contributors to catalyst degradation in DMFCs.

Therefore, considerable attention has been paid to reducing the catalysts agglomeration

and dissolution. Pt/Ru supported on TiO2 embedded carbon nanofibers (Pt‐Ru/TECNF),

was reported as a highly active catalyst for methanol oxidation, which demonstrated re‐

duced agglomeration compared to the conventional Pt catalysts supported on carbon

[178,179]. A study reported that using ethanol solvent as catalyst ink for anode catalyst

increased the interaction between Pt particles and ionomer, resulting in reduced agglom‐

eration [180]. A similar study reported that using N‐methyl pyrrolidone and dimethyl

sulfoxide as catalyst ink enables the reduction of catalysts agglomeration [181]. Polyani‐

line‐Silica (PANI‐SiO2) nanocomposite was created as a support for improving the per‐

formance of Pt/Ni electrocatalysts, to improve catalyst stability. The Pt/Ni/SiO2‐PANI

electrocatalyst demonstrated exceptional catalytic activity. PANI‐SiO2, as an organic–in‐

organic hybrid catalyst support, significantly increased the stability and CO poisoning

tolerance of the resultant electrocatalyst, according to experimental and theoretical data

[182]. A thin, permeable silicon oxide (SiOx) nanomembrane encapsulates a well‐defined

Pt thin film (SiOx/Pt), is used as a catalyst‐coated membrane to improve durability. The

proposed catalyst demonstrated exceptional CO tolerance and highly active methanol ox‐

idation, which also shows an improved lifespan compared to conventional catalyst [183].

TiO2‐Fe2O3@SiO2‐incorporated graphene oxide nanohybrid prepared by the hydrothermal

method was used as a catalyst for DMFC. The nanohybrid showed greater stability with

91.58% retaining the initial current density later on 5000 s in the life span current–time

curve [184]. Nickel–palladium supported onto mesostructured silica nanoparticles (NiPd–

MSN) was used as an electrocatalyst for DMFC. The results of the study showed greater

stability toward oxidation with 61% current retention and superior tolerance to the carbo‐

naceous species accumulation compared with other electrocatalysts [185]. Poly(3,4‐ethyl)

(PEDOT) backed with carbon‐supported Pt is used as anode catalysts for DMFC methanol

oxidation which exhibits high mass activity and superior stability after 500 durability cy‐

cles, which is greater than those of commercial Pt/C catalyst [186]. A study demonstrated

a dual‐template approach to produce well‐defined cage‐bell nanostructures containing Pt

core and a mesoporous PtM (M ¼ Co, Ni) bimetallic shell (Pt@mPtM (M ¼ Co, Ni) CB).

The unique nanostructure and bimetallic properties of Pt@mPtM (M ¼ Co, Ni) CBs

showed higher catalytic activity, superior durability, and greater CO tolerance for the

methanol oxidation reaction than commercial Pt/C [187].

3.3. Gas Diffusion Layer

GDL is the most often overlooked cell component subjected to degradation in the

DMFC system. This is attributed to the fact that the GDL degradation is much limited by

the factors such as cell potential, porosity, and the effect due to the temperature.

3.3.1. Cell Potential

The diffusion layers are usually made of a carbon cloth or carbon paper that contrib‐

utes a substantial role to the species transportation and structural integrity of MEA for

PEM and any alcohol fuel cells [188]. The carbon base provides DMFCs with fairly good

electrical conductivity between the catalyst and current collecting plates [189]. In general,

GDL is around 100–400 μm thick and porous, which permits gas diffusion to the catalyst.

Thinner layers are normally better as they possess nominal electrical resistance and let

fuel and oxidants effortlessly pass through [190]. Nevertheless, carbon corrosion occurs at

different voltage rates under several fuel cell operating conditions; however, the severity


is low compared to a H2‐based PEM fuel cell as the nominal operating voltage is low for

DMFC [191].

3.3.2. Porosity

GDL porosity can also be one of the parameters that can impact its durability and

performance. The GDL is frequently wet‐proofed with a hydrophobic material such as

Teflon® (PTFE). The hydrophobic material permits excess water rejection, thereby inhibit‐

ing flooding [192,193]. The primary physical parameters influencing GDL degradation are

the gas permeability and the pore size diameter [194]. A study reported that the optimal

pore size diameter to be around 25–40 μm, and greater than that would result in excess

flooding, which degrades the GDL; however, increased porosity increases the current

density [195]. The Teflon® content and GDL thickness thus proven to have a larger impact

on GDL degradation just than the porosity [196].

3.3.3. Operating Temperature

Limited water diffusion through the cathode GDL leads to flooding, and too much

water diffusion can lead to cathode active layer and the polymer membrane dry triggering

excessive cell resistance, which is called Ohmic polarization [197]. An increase in cell tem‐

perature than the standard defined level (60–100 °C) tends to dry the GDL, which conse‐

quently results in degradation [198]. On the other hand, low operating temperature is af‐

fected due to the progressive damage in carbon fiber and due to the change in the struc‐

ture of the microporous layer [199]. Nevertheless, at higher operating temperatures, in‐

herent mechanical characteristics of the GDL were drastically affected by the temperature‐

dependent parameters of the PTFE and epoxy resin resulting in a considerable reduction

in resistance to GDL compression than found at lower operating temperatures [200].

3.3.4. Mitigation Strategies of GDL Degradation

The critical aspect impeding the output performance of conventional DMFCs is the

minimum efficiency of the mass transport of oxygen, which is often a result of water flood‐

ing. Currently, researchers are largely determined on the water back diffusion from the

cathode to the anode, as this can potentially solve the flooding at the cathode and decrease

methanol crossover. A new hybrid catalyst layer (CL) was described in a study where

relatively hydrophobic and hydrophilic CLs were integrated to form a hybrid CL [201].

The results of the study showed that the hydrophilic and hydrophobic control can effi‐

ciently generate a better distribution of methanol and water concentration. A three‐di‐

mensional graphene framework was applied to manufacture cathode MPL for improving

water management [202]. The results indicated that the performance and stability were

improved remarkably. From the literature review, water back diffusion improvement is

an efficient approach for water management, inhibiting cathode flooding and reducing

the MCO from the anode to the cathode. Though substantial improvements have been

attained using the aforesaid techniques, the oxygen mass transport within the catalyst

layer is however a challenge. A trilaminar‐catalytic layered GDL design could accelerate

the water back diffusion and encourage oxygen mass transportation. In a study, a trilami‐

nar‐catalytic layer comprises an inner, middle, and outer layer that is used for DMFC

[203]. The middle layer has lower porosity compared to the inner and outer layers. This

produces a water pressure gradient between the inner and middle layers and an oxygen

concentration gradient between the outer and middle layers. Thus, the trilaminar‐catalytic

layered MEA can enhance water back diffusion from the cathode to the anode, as well as

oxygen mass transportation, by creating beneficial gradients. An optimized MPL design

is crucial to mitigate methanol crossover and improve DMFC performance. A study on

the effects of MPL design in a DMFC indicated that anode MPL decreases the methanol

concentration and liquid saturation in the anode CL. Cathode MPL improves the water

back‐flow from the cathode to the anode and Hydrophobic anode CL improves the water


back‐flow from the cathode to anode [204]. A study on the effect of porosity of the copper‐

fibre sintered felt (CFSF) demonstrated that GDL with a super‐hydrophobic pattern that

has a porosity of 60% attains the best performance compared to those of )% and 80% po‐

rous, since it facilitates water removal when the water balance coefficient (WBC) is high

[205].

4. Influence of Water Flooding in MEA Degradation

Cathode flooding of DMFC is a key contributor to the recoverable operational losses

in DMFCs. Cathode flooding is categorized as catalyst flooding and backing flooding.

Catalyst flooding is associated with several ORR active sites, the catalyst thickness, pore

size, and its distribution [206]. The backing flooding is associated with the hydrophobicity

and porosity of the backing layer [207]. Figure 10 [208] depicts the schematic representa‐

tion of the water flooding mechanism in DMFC. The effect of cathode flooding in DMFC

is considerably hazardous than a PEMFC, because of the aqueous methanol feed in the

anode [209]. Almost 80% of the overall water content of DMFC cathode originates from

the anode side, primarily through diffusion and electro‐osmotic drag processes. This

mostly degrades the initial fuel cell efficiency and also leads to excessive voltage drop

rates throughout prolonged operation [210].

Figure 10. Water flooding mechanism in DMFC [208].

In general, DMFCs provide stable performance during the initial phase of a durabil‐

ity test. However, when the operating period is expanded, voltage loss is accelerated ow‐

ing to water accumulation [211]. Water flooding intensifies with time and is known to

effectively halt the operation of DMFC after only a few hundred hours of operation, par‐

ticularly while catalyst‐coated membrane (CCM)‐type MEAs are employed. The follow‐

ing performance recovery of a DMFC can be achieved by cathode drying over longer du‐

rations, that could be as extensive as a few days [212]. Water flooding in a DMFC is com‐

monly ascribed to a lack of hydrophobicity in the cathode GDL/MPL due to the dispersion

of the poly‐tetrafluoroethylene (PTFE) additive [213]. However, emphasizing the loss of

GDL hydrophobic character as the sole reason over such an early phase of cathode flood‐

ing acceleration led to a misinterpretation of the precise accelerated rate of structural

changes of GDL and potentially trigger an overlook of the significant contribution by mor‐

phological changes in the CCL [214]. In a study, using the Sessile‐drop method, it is ob‐

served that decreasing hydrophobicity leads to a small contact angle of water droplets in

the GDL fibers [215]. Despite the irreversible performance reduction, there is a chance that

the physical degradation of electrodes, especially the cathode, will have implications for

water drainage characteristics during a prolonged test, potentially increasing the water


flooding conflict [216]. However, the number of lite is limited with linked water flooding

behavior to morphological alterations in the CCL during protracted DMFC operation.

5. Conclusions

The DMFCs have the potential to play an important role in the future, specifically in

replacing the Li‐ion‐based batteries for able and military applications. Inadequate relia‐

bility can potentially impede the commercialization of DMFCs. As a consequence, a relia‐

bility assessment can provide more insight into the component’s attributes. Therefore, the

present assessment emphasized the general degradation mechanism of MEA components

of DMFCs. Incidentally, the durability of the MEA components needs to be circumvented

for these systems to penetrate the market; specifically, the long‐term durability of these

systems should range from 3000 to 5000 operating hours. Aside from the durability of

MEA components, operational methods and design can have a substantial influence on

the durability characteristics of MEA, which might be a prerequisite for MEA robustness.

This critical assessment can improve the reliability and, subsequently, complement the

market penetration at a faster rate through a structured procedure which can be poten‐

tially useful for DMFC research. In this work, the reliability analysis is also carried out

with the basic structured procedure, while excluding the system modelling and quantita‐

tive/qualitative analysis.

The authors believe that a systematic root cause analysis or a fault tree analysis (FTA)

method of the present literature can help DMFC researchers and manufacturers to gain a

holistic insight into the durability mechanism in a simple yet effective manner.

Author Contributions: Conceptualization, A.J., D.K.M. and N.M.K.; resources, A.J. and N.M.K.;

data curation, A.J. and N.M.K.; writing—original draft preparation, A.J., D.K.M. and N.M.K.; writ‐

ing—review and editing, A.J. and N.M.K.; visualization, D.K.M.; supervision, N.M.K.; project ad‐

ministration, A.J. and N.M.K. All authors have read and agreed to the published version of the

manuscript.

Funding: This research received no external funding.

Institutional Review Board Statement: Not applicable.

Informed Consent Statement: Not applicable.

Data Availability Statement: Not applicable.

Acknowledgments: The author(s) would like to acknowledge the technical support from SusSo

Foundation Cares, a Non‐profitable Organization (NPO), India.

Conflicts of Interest: The authors declare no conflicts of interest.

References

1. Chakraborty, S.; Kumar, N.M.; Jayakumar, A.; Dash, S.K.; Elangovan, D. Selected Aspects of Sustainable Mobility Reveals Im‐

plementable Approaches and Conceivable Actions. Sustainability 2021, 13, 12918. https://doi.org/10.3390/su132212918.

2. Jayakumar, A. An Assessment on Polymer Electrolyte Membrane Fuel Cell Stack Components. In Applied Physical Chemistry

with Multidisciplinary Approaches; Apple Academic Press: Cambridge, MA, USA, 2018; ISBN 978‐1‐315‐16941‐5.

3. Sun, C.; Negro, E.; Vezzù, K.; Pagot, G.; Cavinato, G.; Nale, A.; Herve Bang, Y.; Di Noto, V. Hybrid Inorganic‐Organic Proton‐

Conducting Membranes Based on SPEEK Doped with WO3 Nanoparticles for Application in Vanadium Redox Flow Batteries.

Electrochim. Acta 2019, 309, 311–325. https://doi.org/10.1016/j.electacta.2019.03.056.

4. Garraín, D.; Banacloche, S.; Ferreira‐Aparicio, P.; Martínez‐Chaparro, A.; Lechón, Y. Sustainability Indicators for the Manufac‐

turing and Use of a Fuel Cell Prototype and Hydrogen Storage for Portable Uses. Energies 2021, 14, 6558.

https://doi.org/10.3390/en14206558.

5. Cost‐Effective Iron‐Based Aqueous Redox Flow Batteries for Large‐Scale Energy Storage Application: A Review. J. Power Sources

2021, 493, 229445. https://doi.org/10.1016/j.jpowsour.2020.229445.

6. Wu, F.; Maier, J.; Yu, Y. Guidelines and Trends for Next‐Generation Rechargeable Lithium and Lithium‐Ion Batteries. Chem.

Soc. Rev. 2020, 49, 1569–1614. https://doi.org/10.1039/C7CS00863E.

7. Staffell, I.; Scamman, D.; Abad, A.V.; Balcombe, P.; Dodds, P.E.; Ekins, P.; Shah, N.; Ward, K.R. The Role of Hydrogen and Fuel

Cells in the Global Energy System. Energy Environ. Sci. 2019, 12, 463–491. https://doi.org/10.1039/C8EE01157E.


8. Halme, A.; Selkäinaho, J.; Noponen, T.; Kohonen, A. An Alternative Concept for DMFC—Combined Electrolyzer and H2

PEMFC. Int. J. Hydrog. Energy 2016, 41, 2154–2164. https://doi.org/10.1016/j.ijhydene.2015.12.007.

9. Munjewar, S.S.; Thombre, S.B.; Patil, A.P. Passive Direct Alcohol Fuel Cell Using Methanol and 2‐Propanol Mixture as a Fuel.

Ionics 2019, 25, 2231–2241. https://doi.org/10.1007/s11581‐018‐2627‐y.

10. Cheng, Y.; Zhang, J.; Lu, S.; Jiang, S.P. Significantly Enhanced Performance of Direct Methanol Fuel Cells at Elevated Temper‐

atures. J. Power Sources 2020, 450, 227620. https://doi.org/10.1016/j.jpowsour.2019.227620.

11. Dao, D.V.; Adilbish, G.; Le, T.D.; Nguyen, T.T.D.; Lee, I.‐H.; Yu, Y.‐T. Au@CeO2 Nanoparticles Supported Pt/C Electrocatalyst

to Improve the Removal of CO in Methanol Oxidation Reaction. J. Catal. 2019, 377, 589–599.

https://doi.org/10.1016/j.jcat.2019.07.054.

12. Badwal, S.P.S.; Giddey, S.; Kulkarni, A.; Goel, J.; Basu, S. Direct Ethanol Fuel Cells for Transport and Stationary Applications—

A Comprehensive Review. Appl. Energy 2015, 145, 80–103. https://doi.org/10.1016/j.apenergy.2015.02.002.

13. Pan, Z.; Bi, Y.; An, L. Mathematical Modeling of Direct Ethylene Glycol Fuel Cells Incorporating the Effect of the Competitive

Adsorption. Appl. Therm. Eng. 2019, 147, 1115–1124. https://doi.org/10.1016/j.applthermaleng.2018.10.073.

14. Chu, Y.H.; Shul, Y.G. Combinatorial Investigation of Pt–Ru–Sn Alloys as an Anode Electrocatalysts for Direct Alcohol Fuel

Cells. Int. J. Hydrog. Energy 2010, 35, 11261–11270. https://doi.org/10.1016/j.ijhydene.2010.07.062.

15. Achmad, F.; Kamarudin, S.K.; Daud, W.R.W.; Majlan, E.H. Passive Direct Methanol Fuel Cells for Portable Electronic Devices.

Appl. Energy 2011, 88, 1681–1689. https://doi.org/10.1016/j.apenergy.2010.11.012.

16. Bahrami, H.; Faghri, A. Review and Advances of Direct Methanol Fuel Cells: Part II: Modeling and Numerical Simulation. J.

Power Sources 2013, 230, 303–320. https://doi.org/10.1016/j.jpowsour.2012.12.009.

17. Mallick, R.K.; Thombre, S.B.; Shrivastava, N.K. Vapor Feed Direct Methanol Fuel Cells (DMFCs): A Review. Renew. Sustain.

Energy Rev. 2016, 56, 51–74. https://doi.org/10.1016/j.rser.2015.11.039.

18. Falcão, D.S.; Oliveira, V.B.; Rangel, C.M.; Pinto, A.M.F.R. Review on Micro‐Direct Methanol Fuel Cells. Renew. Sustain. Energy

Rev. 2014, 34, 58–70. https://doi.org/10.1016/j.rser.2014.03.004.

19. Karimi, M.B.; Mohammadi, F.; Hooshyari, K. Recent Approaches to Improve Nafion Performance for Fuel Cell Applications: A

Review. Int. J. Hydrog. Energy 2019, 44, 28919–28938. https://doi.org/10.1016/j.ijhydene.2019.09.096.

20. Lufrano, F.; Baglio, V.; Staiti, P.; Antonucci, V.; Arico’, A.S. Performance Analysis of Polymer Electrolyte Membranes for Direct

Methanol Fuel Cells. J. Power Sources 2013, 243, 519–534. https://doi.org/10.1016/j.jpowsour.2013.05.180.

21. Pethaiah, S.S.; Arunkumar, J.; Ramos, M.; Al‐Jumaily, A.; Manivannan, N. The Impact of Anode Design on Fuel Crossover of

Direct Ethanol Fuel Cell. Bull. Mater. Sci. 2016, 39, 273–278. https://doi.org/10.1007/s12034‐015‐1130‐6.

22. Kumar, P.; Dutta, K.; Das, S.; Kundu, P.P. An Overview of Unsolved Deficiencies of Direct Methanol Fuel Cell Technology:

Factors and Parameters Affecting Its Widespread Use. Int. J. Energy Res. 2014, 38, 1367–1390. https://doi.org/10.1002/er.3163.

23. Park, J.‐Y.; Park, K.‐Y.; Kim, K.B.; Na, Y.; Cho, H.; Kim, J.‐H. Influence and Mitigation Methods of Reaction Intermediates on

Cell Performance in Direct Methanol Fuel Cell System. J. Power Sources 2011, 196, 5446–5452. https://doi.org/10.1016/j.jpow‐

sour.2011.01.108.

24. Bresciani, F.; Rabissi, C.; Zago, M.; Gazdzicki, P.; Schulze, M.; Guétaz, L.; Escribano, S.; Bonde, J.L.; Marchesi, R.; Casalegno, A.

A Combined In‐Situ and Post‐Mortem Investigation on Local Permanent Degradation in a Direct Methanol Fuel Cell. J. Power

Sources 2016, 306, 49–61. https://doi.org/10.1016/j.jpowsour.2015.11.105.

25. Kreuer, K.‐D. Ion Conducting Membranes for Fuel Cells and Other Electrochemical Devices. Chem. Mater. 2014, 26, 361–380.

https://doi.org/10.1021/cm402742u.

26. Ahmad, H.; Kamarudin, S.K.; Hasran, U.A.; Daud, W.R.W. Overview of Hybrid Membranes for Direct‐Methanol Fuel‐Cell Ap‐

plications. Int. J. Hydrog. Energy 2010, 35, 2160–2175. https://doi.org/10.1016/j.ijhydene.2009.12.054.

27. Kim, D.S.; Guiver, M.; McGrath, J.; Pivovar, B.; Kim, Y.S. Molecular Design Aspect of Sulfonated Polymers for Direct Methanol

Fuel Cells. ECS Trans. 2010, 33, 711. https://doi.org/10.1149/1.3484566.

28. Sharma, S. Membranes for Low Temperature Fuel Cells: New Concepts, Single‐Cell Studies and Applications; De Gruyter: Berlin, Ger‐

many, 2019; ISBN 978‐3‐11‐064732‐7.

29. Lin, H.‐L.; Wang, S.‐H. Nafion/Poly(Vinyl Alcohol) Nano‐Fiber Composite and Nafion/Poly(Vinyl Alcohol) Blend Membranes

for Direct Methanol Fuel Cells. J. Membr. Sci. 2014, 452, 253–262. https://doi.org/10.1016/j.memsci.2013.09.039.

30. Choi, J.S.; Sohn, J.‐Y.; Shin, J. A Comparative Study on EB‐Radiation Deterioration of Nafion Membrane in Water and Isopro‐

panol Solvents. Energies 2015, 8, 5370–5380. https://doi.org/10.3390/en8065370.

31. Aydın Ünal, F.; Erduran, V.; Timuralp, C.; Şen, F. 15–Fabrication and Properties of Polymer Electrolyte Membranes (PEM) for

Direct Methanol Fuel Cell Application. In Nanomaterials for Direct Alcohol Fuel Cells; Şen, F., Ed.; Micro and Nano Technologies;

Elsevier: Amsterdam, The Netherlands, 2021; pp. 283–302, ISBN 978‐0‐12‐821713‐9.

32. Ercelik, M.; Ozden, A.; Devrim, Y.; Colpan, C.O. Investigation of Nafion Based Composite Membranes on the Performance of

DMFCs. Int. J. Hydrog. Energy 2017, 42, 2658–2668. https://doi.org/10.1016/j.ijhydene.2016.06.215.

33. Wang, J.; Liao, J.; Yang, L.; Zhang, S.; Huang, X.; Ji, J. Highly Compatible Acid–Base Blend Membranes Based on Sulfonated

Poly(Ether Ether Ketone) and Poly(Ether Ether Ketone‐Alt‐Benzimidazole) for Fuel Cells Application. J. Membr. Sci. 2012, 415–

416, 644–653. https://doi.org/10.1016/j.memsci.2012.05.045.

34. Liu, C.; Wang, X.; Xu, J.; Wang, C.; Chen, H.; Liu, W.; Chen, Z.; Du, X.; Wang, S.; Wang, Z. PEMs with High Proton Conductivity

and Excellent Methanol Resistance Based on Sulfonated Poly (Aryl Ether Ketone Sulfone) Containing Comb‐Shaped Structures

for DMFCs Applications. Int. J. Hydrog. Energy 2020, 45, 945–957. https://doi.org/10.1016/j.ijhydene.2019.10.166.


35. Dutta, K.; Das, S.; Kundu, P.P. Synthesis, Preparation, and Performance of Blends and Composites of π‐Conjugated Polymers

and Their Copolymers in DMFCs. Polym. Rev. 2015, 55, 630–677. https://doi.org/10.1080/15583724.2015.1028631.

36. Kludský, M.; Vopička, O.; Matějka, P.; Hovorka, Š.; Friess, K. Nafion® Modified with Primary Amines: Chemical Structure,

Sorption Properties and Pervaporative Separation of Methanol‐Dimethyl Carbonate Mixtures. Eur. Polym. J. 2018, 99, 268–276.

https://doi.org/10.1016/j.eurpolymj.2017.12.028.

37. Klose, C.; Breitwieser, M.; Vierrath, S.; Klingele, M.; Cho, H.; Büchler, A.; Kerres, J.; Thiele, S. Electrospun Sulfonated Poly(Ether

Ketone) Nanofibers as Proton Conductive Reinforcement for Durable Nafion Composite Membranes. J. Power Sources 2017, 361,

237–242. https://doi.org/10.1016/j.jpowsour.2017.06.080.

38. Pérez, L.C.; Brandão, L.; Sousa, J.M.; Mendes, A. Segmented Polymer Electrolyte Membrane Fuel Cells—A Review. Renew.

Sustain. Energy Rev. 2011, 15, 169–185. https://doi.org/10.1016/j.rser.2010.08.024.

39. Prokop, M.; Kodym, R.; Bystron, T.; Drakselova, M.; Paidar, M.; Bouzek, K. Degradation Kinetics of Pt during High‐Tempera‐

ture PEM Fuel Cell Operation Part II: Dissolution Kinetics of Pt Incorporated in a Catalyst Layer of a Gas‐Diffusion Electrode.

Electrochim. Acta 2020, 333, 135509. https://doi.org/10.1016/j.electacta.2019.135509.

40. Kamarudin, S.K.; Hashim, N. Materials, Morphologies and Structures of MEAs in DMFCs. Renew. Sustain. Energy Rev. 2012, 16,

2494–2515. https://doi.org/10.1016/j.rser.2012.01.073.

41. Xinyao, Y.; Zhongqing, J.; Yuedong, M. Preparation of Anodes for DMFC by Co‐Sputtering of Platinum and Ruthenium. Plasma

Sci. Technol. 2010, 12, 224–229. https://doi.org/10.1088/1009‐0630/12/2/18.

42. Dutta, K.; Das, S.; Rana, D.; Kundu, P.P. Enhancements of Catalyst Distribution and Functioning Upon Utilization of Conduct‐

ing Polymers as Supporting Matrices in DMFCs: A Review. Polym. Rev. 2015, 55, 1–56.

https://doi.org/10.1080/15583724.2014.958771.

43. Gulaboski, R.; Mirceski, V.; Komorsky‐Lovric, S.; Lovric, M. Three‐Phase Electrodes: Simple and Efficient Tool for Analysis of

Ion Transfer Processes across Liquid‐Liquid Interface—Twenty Years On. J Solid State Electrochem. 2020, 24, 2575–2583.

https://doi.org/10.1007/s10008‐020‐04629‐8.

44. Li, Q.; Wang, T.; Havas, D.; Zhang, H.; Xu, P.; Han, J.; Cho, J.; Wu, G. High‐Performance Direct Methanol Fuel Cells with

Precious‐Metal‐Free Cathode. Adv. Sci. 2016, 3, 1600140. https://doi.org/10.1002/advs.201600140.

45. Sgroi, M.F.; Zedde, F.; Barbera, O.; Stassi, A.; Sebastián, D.; Lufrano, F.; Baglio, V.; Aricò, A.S.; Bonde, J.L.; Schuster, M. Cost

Analysis of Direct Methanol Fuel Cell Stacks for Mass Production. Energies 2016, 9, 1008. https://doi.org/10.3390/en9121008.

46. Samad, S.; Loh, K.S.; Wong, W.Y.; Lee, T.K.; Sunarso, J.; Chong, S.T.; Wan Daud, W.R. Carbon and Non‐Carbon Support Mate‐

rials for Platinum‐Based Catalysts in Fuel Cells. Int. J. Hydrog. Energy 2018, 43, 7823–7854.

https://doi.org/10.1016/j.ijhydene.2018.02.154.

47. Khotseng, L. Oxygen Reduction Reaction; IntechOpen: Gujarat, India, 2018; ISBN 978‐1‐78984‐813‐7.

48. Yan, X.H.; Zhao, T.S.; An, L.; Zhao, G.; Zeng, L. A Crack‐Free and Super‐Hydrophobic Cathode Micro‐Porous Layer for Direct

Methanol Fuel Cells. Appl. Energy 2015, 138, 331–336. https://doi.org/10.1016/j.apenergy.2014.10.044.

49. Abdelkareem, M.A.; Sayed, E.T.; Nakagawa, N. Significance of Diffusion Layers on the Performance of Liquid and Vapor Feed

Passive Direct Methanol Fuel Cells. Energy 2020, 209, 118492. https://doi.org/10.1016/j.energy.2020.118492.

50. Ivanova, N.A.; Alekseeva, O.K.; Fateev, V.N.; Shapir, B.L.; Spasov, D.D.; Nikitin, S.M.; Presnyakov, M.Yu.; Kolobylina, N.N.;

Soloviev, M.A.; Mikhalev, A.I.; et al. Activity and Durability of Electrocatalytic Layers with Low Platinum Loading Prepared

by Magnetron Sputtering onto Gas Diffusion Electrodes. Int. J. Hydrog. Energy 2019, 44, 29529–29536.


51. Netzeband, C.; Arlt, T.; Wippermann, K.; Lehnert, W.; Manke, I. Three‐Dimensional Multiscale Analysis of Degradation of

Nano‐ and Micro‐Structure in Direct Methanol Fuel Cell Electrodes after Methanol Starvation. J. Power Sources 2016, 327, 481–

487. https://doi.org/10.1016/j.jpowsour.2016.07.094.

52. Nagy, K.A.; Tóth, I.Y.; Ballai, G.; Varga, Á.T.; Szenti, I.; Sebők, D.; Kopniczky, J.; Hopp, B.; Kukovecz, Á. Wetting and Evapora‐

tion on a Carbon Cloth Type Gas Diffusion Layer for Passive Direct Alcohol Fuel Cells. J. Mol. Liq. 2020, 304, 112698.

https://doi.org/10.1016/j.molliq.2020.112698.

53. Poplavsky, V.V.; Dorozhko, A.V.; Matys, V.G. Ion‐Beam Formation of Electrocatalysts for Fuel Cells with Polymer Membrane

Electrolyte. J. Synch. Investig. 2017, 11, 326–332. https://doi.org/10.1134/S1027451017020124.

54. Liu, G.; Li, X.; Wang, M.; Wang, M.; Kim, J.Y.; Woo, J.Y.; Wang, X.; Lee, J.K. A Study on Anode Diffusion Layer for Performance

Enhancement of a Direct Methanol Fuel Cell. Energy Convers. Manag. 2016, 126, 697–703. https://doi.org/10.1016/j.encon‐

man.2016.08.067.

55. Falcão, D.S.; Silva, R.A.; Rangel, C.M.; Pinto, A.M.F.R. Performance of an Active Micro Direct Methanol Fuel Cell Using Reduced

Catalyst Loading MEAs. Energies 2017, 10, 1683. https://doi.org/10.3390/en10111683.

56. Hsieh, S.‐S.; Hung, L.‐C.; Liu, C.‐C.; Huang, C.‐F. Analyses of Electrochemical Impedance Spectroscopy and Cyclic Voltamme‐

try in Micro‐Direct Methanol Fuel Cell Stacks. Int. J. Energy Res. 2016, 40, 2162–2175. https://doi.org/10.1002/er.3597.

57. Rashed, M.K.; Mohd Salleh, M.A.; Abdulbari, H.A.; Shah Ismail, M.H.; Izhar, S. The Effects of Electrode and Catalyst Selection

on Microfluidic Fuel Cell Performance. ChemBioEng Rev. 2015, 2, 356–372. https://doi.org/10.1002/cben.201500007.

58. Gauthier, E.; Benziger, J.B. Gas Management and Multiphase Flow in Direct Alcohol Fuel Cells. Electrochim. Acta 2014, 128, 238–

247. https://doi.org/10.1016/j.electacta.2013.09.047.

59. Xue, R.; Zhang, Y.; Liu, X. A Novel Cathode Gas Diffusion Layer for Water Management of Passive μ‐DMFC. Energy 2017, 139,

535–541. https://doi.org/10.1016/j.energy.2017.08.016.


60. Yuan, W.; Tang, Y.; Yang, X.; Liu, B.; Wan, Z. Structural Diversity and Orientation Dependence of a Liquid‐Fed Passive Air‐

Breathing Direct Methanol Fuel Cell. Int. J. Hydrog. Energy 2012, 37, 9298–9313. https://doi.org/10.1016/j.ijhydene.2012.03.013.

61. Yi, P.; Peng, L.; Lai, X.; Li, M.; Ni, J. Investigation of Sintered Stainless Steel Fiber Felt as Gas Diffusion Layer in Proton Exchange

Membrane Fuel Cells. Int. J. Hydrog. Energy 2012, 37, 11334–11344. https://doi.org/10.1016/j.ijhydene.2012.04.161.

62. Zhao, Z.; Zhang, F.; Zhang, Y.; Zhang, D. Performance Optimization of ΜDMFC with Foamed Stainless Steel Cathode Current

Collector. Energies 2021, 14, 6608. https://doi.org/10.3390/en14206608.

63. Zhang, J.; Zhu, Y.L.; Qi, G.; Li, J.Y. Current Development of Key Materials for Low Temperature Fuel Cells. Key Eng. Mater.

2017, 727, 670–677. https://doi.org/10.4028/www.scientific.net/KEM.727.670.

64. Madheswaran, D.K.; Jayakumar, A. Recent Advancements on Non‐Platinum Based Catalyst Electrode Material for Polymer

Electrolyte Membrane Fuel Cells: A Mini Techno‐Economic Review. Bull. Mater. Sci. 2021, 44, 287.

https://doi.org/10.1007/s12034‐021‐02572‐6.

65. Yao, D.; Jao, T.‐C.; Zhang, W.; Xu, L.; Xing, L.; Ma, Q.; Xu, Q.; Li, H.; Pasupathi, S.; Su, H. In‐Situ Diagnosis on Performance

Degradation of High Temperature Polymer Electrolyte Membrane Fuel Cell by Examining Its Electrochemical Properties under

Operation. Int. J. Hydrog. Energy 2018, 43, 21006–21016. https://doi.org/10.1016/j.ijhydene.2018.09.103.

66. Han, J.; Han, J.; Yu, S. Experimental Analysis of Performance Degradation of 3‐Cell PEMFC Stack under Dynamic Load Cycle.

Int. J. Hydrog. Energy 2020, 45, 13045–13054. https://doi.org/10.1016/j.ijhydene.2020.02.215.

67. Chu, T.; Zhang, R.; Wang, Y.; Ou, M.; Xie, M.; Shao, H.; Yang, D.; Li, B.; Ming, P.; Zhang, C. Performance Degradation and

Process Engineering of the 10 KW Proton Exchange Membrane Fuel Cell Stack. Energy 2021, 219, 119623.

https://doi.org/10.1016/j.energy.2020.119623.

68. Casalegno, A.; Bresciani, F.; Zago, M.; Marchesi, R. Experimental Investigation of Methanol Crossover Evolution during Direct

Methanol Fuel Cell Degradation Tests. J. Power Sources 2014, 249, 103–109. https://doi.org/10.1016/j.jpowsour.2013.10.032.

69. Shrivastava, N.K.; Chadge, R.B.; Bankar, S.L. Modelling and Simulation of Passive Feed Direct Methanol Fuel Cell. Int. J. Energy

Technol. Policy 2017, 13, 4–18. https://doi.org/10.1504/IJETP.2017.080610.

70. Direct Methanol Fuel Cell Methanol and Water Crossover. Available online: https://www.wpclipart.com/sci‐

ence/how_things_work/Direct_Methanol_Fuel_Cell__Methanol_and_Water_Crossover.png.html (accessed on 13 November

2021).

71. Xu, C.; Faghri, A.; Li, X.; Ward, T. Methanol and Water Crossover in a Passive Liquid‐Feed Direct Methanol Fuel Cell. Int. J.

Hydrog. Energy 2010, 35, 1769–1777. https://doi.org/10.1016/j.ijhydene.2009.12.055.

72. Sharifi, S.; Rahimi, R.; Mohebbi‐Kalhori, D.; Colpan, C.O. Numerical Investigation of Methanol Crossover through the Mem‐

brane in a Direct Methanol Fuel Cell. Iran. J. Hydrog. Fuel Cell 2018, 5, 21–33. https://doi.org/10.22104/ijhfc.2018.2867.1170.

73. Chi, N.T.Q.; Bae, B.; Kim, D. Electro‐Osmotic Drag Effect on the Methanol Permeation for Sulfonated Poly(Ether Ether Ketone)

and Nafion117 Membranes. J. Nanosci. Nanotechnol. 2013, 13, 7529–7534. https://doi.org/10.1166/jnn.2013.7894.

74. García‐Nieto, D.; Barragán, V.M. A Comparative Study of the Electro‐Osmotic Behavior of Cation and Anion Exchange Mem‐

branes in Alcohol‐Water Media. Electrochim. Acta 2015, 154, 166–176. https://doi.org/10.1016/j.electacta.2014.12.070.

75. Endo, N.; Ogawa, Y.; Ukai, K.; Kakihana, Y.; Higa, M. DMFC Performance of Polymer Electrolyte Membranes Prepared from a

Graft‐Copolymer Consisting of a Polysulfone Main Chain and Styrene Sulfonic Acid Side Chains. Energies 2016, 9, 658.

https://doi.org/10.3390/en9080658.

76. Huang, K.‐L.; Liao, Y.‐H.; Chen, S.‐J. Effects of Operating Parameters on Gas‐Phase PAH Emissions from a Direct Methanol

Fuel Cell. Aerosol Air Qual. Res. 2019, 19, 2196–2204. https://doi.org/10.4209/aaqr.2019.08.0388.

77. Yuan, Z.; Chuai, W.; Guo, Z.; Tu, Z.; Kong, F. The Self‐Adaptive Fuel Supply Mechanism in Micro DMFC Based on the Mi‐

crovalve. Micromachines 2019, 10, 353. https://doi.org/10.3390/mi10060353.

78. Araya, S.S.; Andreasen, S.J.; Kær, S.K. Experimental Characterization of the Poisoning Effects of Methanol‐Based Reformate

Impurities on a PBI‐Based High Temperature PEM Fuel Cell. Energies 2012, 5, 4251. https://doi.org/10.3390/en5114251.

79. Bogolowski, N.; Drillet, J.‐F. Appropriate Balance between Methanol Yield and Power Density in Portable Direct Methanol Fuel

Cell. Chem. Eng. J. 2015, 270, 91–100. https://doi.org/10.1016/j.cej.2015.01.104.

80. Ji, F.; Yang, L.; Sun, H.; Wang, S.; Li, H.; Jiang, L.; Sun, G. A Novel Method for Analysis and Prediction of Methanol Mass

Transfer in Direct Methanol Fuel Cell. Energy Convers. Manag. 2017, 154, 482–490. https://doi.org/10.1016/j.encon‐

man.2017.10.083.

81. Ramesh, V.; Krishnamurthy, B. Modeling the Transient Temperature Distribution in a Direct Methanol Fuel Cell. J. Electroanal.

Chem. 2018, 809, 1–7. https://doi.org/10.1016/j.jelechem.2017.12.015.

82. Govindarasu, R.; Somasundaram, S. Studies on Influence of Cell Temperature in Direct Methanol Fuel Cell Operation. Processes

2020, 8, 353. https://doi.org/10.3390/pr8030353.

83. Andoh, S.; Fujita, A.; Miitsu, T.; Kuroda, Y.; Mitsushima, S. Practical and Reliable Methanol Concentration Sensor for Direct

Methanol Fuel Cells. Electrochemistry 2021, https://doi.org/10.5796/electrochemistry.21‐00012.

84. Tsen, W.‐C. Composite Proton Exchange Membranes Based on Chitosan and Phosphotungstic Acid Immobilized One‐Dimen‐

sional Attapulgite for Direct Methanol Fuel Cells. Nanomaterials 2020, 10, 1641. https://doi.org/10.3390/nano10091641.

85. Sudaroli, B.M.; Kolar, A.K. An Experimental Study on the Effect of Membrane Thickness and PTFE (Polytetrafluoroethylene)

Loading on Methanol Crossover in Direct Methanol Fuel Cell. Energy 2016, 98, 204–214. https://doi.org/10.1016/j.en‐

ergy.2015.12.101.


86. Gwak, G.; Lee, K.; Ferekh, S.; Lee, S.; Ju, H. Analyzing the Effects of Fluctuating Methanol Feed Concentration in Active‐Type

Direct Methanol Fuel Cell (DMFC) Systems. Int. J. Hydrog. Energy 2015, 40, 5396–5407.


87. Zhang, C.; Yue, X.; Yang, Y.; Lu, N.; Zhang, S.; Wang, G. Thin and Methanol‐Resistant Reinforced Composite Membrane Based

on Semi‐Crystalline Poly (Ether Ether Ketone) for Fuel Cell Applications. J. Power Sources 2020, 450, 227664.

https://doi.org/10.1016/j.jpowsour.2019.227664.

88. Wippermann, K.; Klafki, K.; Kulikovsky, A.A. In Situ Measurement of the Oxygen Diffusion Coefficient in the Cathode Catalyst

Layer of a Direct Methanol Fuel Cell. Electrochim. Acta 2014, 141, 212–215. https://doi.org/10.1016/j.electacta.2014.06.164.

89. Gago, A.S.; Esquivel, J.‐P.; Sabaté, N.; Santander, J.; Alonso‐Vante, N. Comprehensive Characterization and Understanding of

Micro‐Fuel Cells Operating at High Methanol Concentrations. Beilstein J. Nanotechnol. 2015, 6, 2000–2006.

https://doi.org/10.3762/bjnano.6.203.

90. Zago, M.; Bisello, A.; Baricci, A.; Rabissi, C.; Brightman, E.; Hinds, G.; Casalegno, A. On the Actual Cathode Mixed Potential in

Direct Methanol Fuel Cells. J. Power Sources 2016, 325, 714–722. https://doi.org/10.1016/j.jpowsour.2016.06.093.

91. Majidi, P.; Altarawneh, R.M.; Ryan, N.D.W.; Pickup, P.G. Determination of the Efficiency of Methanol Oxidation in a Direct

Methanol Fuel Cell. Electrochim. Acta 2016, 199, 210–217. https://doi.org/10.1016/j.electacta.2016.03.147.

92. Zhao, X.; Yuan, W.; Wu, Q.; Sun, H.; Luo, Z.; Fu, H. High‐Temperature Passive Direct Methanol Fuel Cells Operating with

Concentrated Fuels. J. Power Sources 2015, 273, 517–521. https://doi.org/10.1016/j.jpowsour.2014.09.128.

93. Wan, N. High Performance Direct Methanol Fuel Cell with Thin Electrolyte Membrane. J. Power Sources 2017, 354, 167–171.

https://doi.org/10.1016/j.jpowsour.2017.04.037.

94. Xue, Y.; Chan, S. Layer‐by‐Layer Self‐Assembly of CHI/PVS–Nafion Composite Membrane for Reduced Methanol Crossover

and Enhanced DMFC Performance. Int. J. Hydrog. Energy 2015, 40, 1877–1885. https://doi.org/10.1016/j.ijhydene.2014.11.129.

95. Rambabu, G.; Bhat, S.D. Carbon‐Polymer Nanocomposite Membranes as Electrolytes for Direct Methanol Fuel Cells. In Mem‐

brane Technology; CRC Press: Boca Raton, FL, USA, 2018; ISBN 978‐1‐315‐10566‐6.

96. Yee, R.S.L.; Zhang, K.; Ladewig, B.P. The Effects of Sulfonated Poly(Ether Ether Ketone) Ion Exchange Preparation Conditions

on Membrane Properties. Membranes 2013, 3, 182–195. https://doi.org/10.3390/membranes3030182.

97. Iannaci, A.; Mecheri, B.; D’Epifanio, A.; Licoccia, S. Sulfated Zirconium Oxide as Electrode and Electrolyte Additive for Direct

Methanol Fuel Cell Applications. Int. J. Hydrog. Energy 2014, 39, 11241–11249. https://doi.org/10.1016/j.ijhydene.2014.05.121.

98. Yang, C.‐C. Fabrication and Characterization of Poly(Vinyl Alcohol)/Montmorillonite/Poly(Styrene Sulfonic Acid) Proton‐Con‐

ducting Composite Membranes for Direct Methanol Fuel Cells. Int. J. Hydrog. Energy 2011, 36, 4419–4431.


99. Maiti, J.; Kakati, N.; Lee, S.H.; Jee, S.H.; Viswanathan, B.; Yoon, Y.S. Where Do Poly(Vinyl Alcohol) Based Membranes Stand in

Relation to Nafion® for Direct Methanol Fuel Cell Applications? J. Power Sources 2012, 216, 48–66. https://doi.org/10.1016/j.jpow‐

sour.2012.05.057.

100. Zhong, S.; Cui, X.; Gao, Y.; Liu, W.; Dou, S. Fabrication and Properties of Poly(Vinyl Alcohol)‐Based Polymer Electrolyte Mem‐

branes for Direct Methanol Fuel Cell Applications. Int. J. Hydrog. Energy 2014, 39, 17857–17864.


101. Sidharthan, K.A.; Joseph, S. Preparation and Characterization of Polyvinyl Alcohol Based Nanocomposite Membrane for Direct

Methanol Fuel Cell. AIP Conf. Proc. 2019, 2162, 020143. https://doi.org/10.1063/1.5130353.

102. Aricò, A.S.; Sebastian, D.; Schuster, M.; Bauer, B.; D’Urso, C.; Lufrano, F.; Baglio, V. Selectivity of Direct Methanol Fuel Cell

Membranes. Membranes 2015, 5, 793–809. https://doi.org/10.3390/membranes5040793.

103. Katzfuß, A.; Poynton, S.; Varcoe, J.; Gogel, V.; Storr, U.; Kerres, J. Methylated Polybenzimidazole and Its Application as a Blend

Component in Covalently Cross‐Linked Anion‐Exchange Membranes for DMFC. J. Membr. Sci. 2014, 465, 129–137.

https://doi.org/10.1016/j.memsci.2014.04.004.

104. Alam, T.M.; Hibbs, M.R. Characterization of Heterogeneous Solvent Diffusion Environments in Anion Exchange Membranes.

Macromolecules 2014, 47, 1073–1084. https://doi.org/10.1021/ma402528v.

105. Xu, W.; Zhao, Y.; Yuan, Z.; Li, X.; Zhang, H.; Vankelecom, I.F.J. Highly Stable Anion Exchange Membranes with Internal Cross‐

Linking Networks. Adv. Funct. Mater. 2015, 25, 2583–2589. https://doi.org/10.1002/adfm.201500284.

106. Verjulio, R.W.; Santander, J.; Ma, J.; Alonso‐Vante, N. Selective CoSe2/C Cathode Catalyst for Passive Air‐Breathing Alkaline

Anion Exchange Membrane μ‐Direct Methanol Fuel Cell (AEM‐ΜDMFC). Int. J. Hydrog. Energy 2016, 41, 19595–19600.


107. Benvenuti, T.; García‐Gabaldón, M.; Ortega, E.M.; Rodrigues, M.A.S.; Bernardes, A.M.; Pérez‐Herranz, V.; Zoppas‐Ferreira, J.

Influence of the Co‐Ions on the Transport of Sulfate through Anion Exchange Membranes. J. Membr. Sci. 2017, 542, 320–328.

https://doi.org/10.1016/j.memsci.2017.08.021.

108. Higa, M.; Mehdizadeh, S.; Feng, S.; Endo, N.; Kakihana, Y. Cell Performance of Direct Methanol Alkaline Fuel Cell (DMAFC)

Using Anion Exchange Membranes Prepared from PVA‐Based Block Copolymer. J. Membr. Sci. 2020, 597, 117618.

https://doi.org/10.1016/j.memsci.2019.117618.

109. Hu, X.; Huang, Y.; Liu, L.; Ju, Q.; Zhou, X.; Qiao, X.; Zheng, Z.; Li, N. Piperidinium Functionalized Aryl Ether‐Free Polyaromat‐

ics as Anion Exchange Membrane for Water Electrolysers: Performance and Durability. J. Membr. Sci. 2021, 621, 118964.

https://doi.org/10.1016/j.memsci.2020.118964.


110. Zakaria, Z.; Kamarudin, S.K. A Review of Quaternized Polyvinyl Alcohol as an Alternative Polymeric Membrane in DMFCs

and DEFCs. Int. J. Energy Res. 2020, 44, 6223–6239. https://doi.org/10.1002/er.5314.

111. Mustain, W.E.; Chatenet, M.; Page, M.; Kim, Y.S. Durability Challenges of Anion Exchange Membrane Fuel Cells. Energy Envi‐

ron. Sci. 2020, 13, 2805–2838. https://doi.org/10.1039/D0EE01133A.

112. Chen, N.; Wang, H.H.; Kim, S.P.; Kim, H.M.; Lee, W.H.; Hu, C.; Bae, J.Y.; Sim, E.S.; Chung, Y.‐C.; Jang, J.‐H.; et al. Poly(Fluorenyl

Aryl Piperidinium) Membranes and Ionomers for Anion Exchange Membrane Fuel Cells. Nat Commun. 2021, 12, 2367.

https://doi.org/10.1038/s41467‐021‐22612‐3.

113. Electrochemical Characteristics of Different Membranes Used for DMFC. Available online: https://www.fu‐

matech.com/EN/Membranes/Fuel‐cells/Products%2Bfumapem/index.html (accessed on 13 November 2021).

114. Chen, X.; Li, T.; Shen, J.; Hu, Z. From Structures, Packaging to Application: A System‐Level Review for Micro Direct Methanol

Fuel Cell. Renew. Sustain. Energy Rev. 2017, 80, 669–678. https://doi.org/10.1016/j.rser.2017.05.272.

115. Xia, Z.; Zhang, X.; Sun, H.; Wang, S.; Sun, G. Recent Advances in Multi‐Scale Design and Construction of Materials for Direct

Methanol Fuel Cells. Nano Energy 2019, 65, 104048. https://doi.org/10.1016/j.nanoen.2019.104048.

116. Yan, X.H.; Gao, P.; Zhao, G.; Shi, L.; Xu, J.B.; Zhao, T.S. Transport of Highly Concentrated Fuel in Direct Methanol Fuel Cells.

Appl. Therm. Eng. 2017, 126, 290–295. https://doi.org/10.1016/j.applthermaleng.2017.07.186.

117. Kim, J.; Jang, J.‐S.; Peck, D.‐H.; Lee, B.; Yoon, S.‐H.; Jung, D.‐H. Methanol‐Tolerant Platinum‐Palladium Catalyst Supported on

Nitrogen‐Doped Carbon Nanofiber for High Concentration Direct Methanol Fuel Cells. Nanomaterials 2016, 6, 148.

https://doi.org/10.3390/nano6080148.

118. Lo Vecchio, C.; Sebastián, D.; Lázaro, M.J.; Aricò, A.S.; Baglio, V. Methanol‐Tolerant M–N–C Catalysts for Oxygen Reduction

Reactions in Acidic Media and Their Application in Direct Methanol Fuel Cells. Catalysts 2018, 8, 650.

https://doi.org/10.3390/catal8120650.

119. Elangovan, A.; Xu, J.; Sekar, A.; Rajendran, S.; Liu, B.; Li, J. Platinum Deposited Nitrogen‐Doped Vertically Aligned Carbon

Nanofibers as Methanol Tolerant Catalyst for Oxygen Reduction Reaction with Improved Durability. Appl. Nano 2021, 2, 303–

318. https://doi.org/10.3390/applnano2040022.

120. Prapainainar, P.; Du, Z.; Theampetch, A.; Prapainainar, C.; Kongkachuichay, P.; Holmes, S.M. Properties and DMFC Perfor‐

mance of Nafion/Mordenite Composite Membrane Fabricated by Solution‐Casting Method with Different Solvent Ratio. Energy

2020, 190, 116451. https://doi.org/10.1016/j.energy.2019.116451.

121. Divya, K.; Sri Abirami Saraswathi, M.S.; Rana, D.; Alwarappan, S.; Nagendran, A. Custom‐Made Sulfonated Poly (Ether Sul‐

fone) Nanocomposite Proton Exchange Membranes Using Exfoliated Molybdenum Disulfide Nanosheets for DMFC Applica‐

tions. Polymer 2018, 147, 48–55. https://doi.org/10.1016/j.polymer.2018.05.054.

122. Barbera, O.; Stassi, A.; Sebastian, D.; Bonde, J.L.; Giacoppo, G.; D’Urso, C.; Baglio, V.; Aricò, A.S. Simple and Functional Direct

Methanol Fuel Cell Stack Designs for Application in Portable and Auxiliary Power Units. Int. J. Hydrog. Energy 2016, 41, 12320–

12329. https://doi.org/10.1016/j.ijhydene.2016.05.135.

123. Wang, L.; Yuan, Z.; Wen, F.; Cheng, Y.; Zhang, Y.; Wang, G. A Bipolar Passive DMFC Stack for Portable Applications. Energy

2018, 144, 587–593. https://doi.org/10.1016/j.energy.2017.12.039.

124. Sombatmankhong, K.; Yunus, K.; Fisher, A.C. Electrocogeneration of Hydrogen Peroxide: Confocal and Potentiostatic Investi‐

gations of Hydrogen Peroxide Formation in a Direct Methanol Fuel Cell. J. Power Sources 2013, 240, 219–231.


125. Li, Y.; Liang, L.; Liu, C.; Li, Y.; Xing, W.; Sun, J. Self‐Healing Proton‐Exchange Membranes Composed of Nafion–Poly(Vinyl

Alcohol) Complexes for Durable Direct Methanol Fuel Cells. Adv. Mater. 2018, 30, 1707146.

https://doi.org/10.1002/adma.201707146.

126. Wang, A.; Yuan, W.; Huang, S.; Tang, Y.; Chen, Y. Structural Effects of Expanded Metal Mesh Used as a Flow Field for a Passive

Direct Methanol Fuel Cell. Appl. Energy 2017, 208, 184–194. https://doi.org/10.1016/j.apenergy.2017.10.052.

127. Sakurai, Y.; Kawai, A. Mechanical Stress Effect on Ionic Conductivity of Perflurosulfonic Acid (PFSA) Film by Photolithography.

J. Photopolym. Sci. Technol. 2012, 25, 723–727. https://doi.org/10.2494/photopolymer.25.723.

128. Yuan, Z.Y.; Zhang, Y.F.; Fu, W.T.; Li, Z.P.; Liu, X.W. Investigation of the Direct Methanol Fuel Cell with Novel Assembly

Method. Fuel Cells 2013, 13, 794–803. https://doi.org/10.1002/fuce.201200082.

129. Ince, A.C.; Karaoglan, M.U.; Glüsen, A.; Colpan, C.O.; Müller, M.; Stolten, D. Semiempirical Thermodynamic Modeling of a

Direct Methanol Fuel Cell System. Int. J. Energy Res. 2019, 43, 3601–3615. https://doi.org/10.1002/er.4508.

130. Li, L.‐Y.; Yu, B.‐C.; Shih, C.‐M.; Lue, S.J. Polybenzimidazole Membranes for Direct Methanol Fuel Cell: Acid‐Doped or Alkali‐

Doped? J. Power Sources 2015, 287, 386–395. https://doi.org/10.1016/j.jpowsour.2015.04.018.

131. Kimiaie, N.; Trappmann, C.; Janßen, H.; Hehemann, M.; Echsler, H.; Müller, M. Influence of Contamination with Inorganic

Impurities on the Durability of a 1 KW DMFC System. Fuel Cells 2014, 14, 64–75. https://doi.org/10.1002/fuce.201300047.

132. Nicotera, I.; Simari, C.; Enotiadis, A. 2—Nafion‐Based Cation‐Exchange Membranes for Direct Methanol Fuel Cells. In Direct

Methanol Fuel Cell Technology; Dutta, K., Ed.; Elsevier: Amsterdam, The Netherlands, 2020; pp. 13–36, ISBN 978‐0‐12‐819158‐3.

133. Wang, L.; Kang, B.; Gao, N.; Du, X.; Jia, L.; Sun, J. Corrosion Behaviour of Austenitic Stainless Steel as a Function of Methanol

Concentration for Direct Methanol Fuel Cell Bipolar Plate. J. Power Sources 2014, 253, 332–341. https://doi.org/10.1016/j.jpow‐

sour.2013.12.043.


134. Simari, C.; Nicotera, I.; Aricò, A.S.; Baglio, V.; Lufrano, F. New Insights into Properties of Methanol Transport in Sulfonated

Polysulfone Composite Membranes for Direct Methanol Fuel Cells. Polymers 2021, 13, 1386.

https://doi.org/10.3390/polym13091386.

135. Lufrano, E.; Simari, C.; Lo Vecchio, C.; Aricò, A.S.; Baglio, V.; Nicotera, I. Barrier Properties of Sulfonated Polysulfone/Layered

Double Hydroxides Nanocomposite Membrane for Direct Methanol Fuel Cell Operating at High Methanol Concentrations. Int.

J. Hydrog. Energy 2020, 45, 20647–20658. https://doi.org/10.1016/j.ijhydene.2020.02.101.

136. Li, J.; Fan, K.; Cai, W.; Ma, L.; Xu, G.; Xu, S.; Ma, L.; Cheng, H. An In‐Situ Nano‐Scale Swelling‐Filling Strategy to Improve

Overall Performance of Nafion Membrane for Direct Methanol Fuel Cell Application. J. Power Sources 2016, 332, 37–41.


137. Li, X.; Miao, Z.; Marten, L.; Blankenau, I. Experimental Measurements of Fuel and Water Crossover in an Active DMFC. Int. J.


138. Mollá, S.; Compañ, V. Polymer Blends of SPEEK for DMFC Application at Intermediate Temperatures. Int. J. Hydrog. Energy

2014, 39, 5121–5136. https://doi.org/10.1016/j.ijhydene.2014.01.085.

139. Krishnan, N.N.; Henkensmeier, D.; Jang, J.H.; Kim, H.‐J. Nanocomposite Membranes for Polymer Electrolyte Fuel Cells. Mac‐

romol. Mater. Eng. 2014, 299, 1031–1041. https://doi.org/10.1002/mame.201300378.

140. Zatoń, M.; Rozière, J.; Jones, D.J. Current Understanding of Chemical Degradation Mechanisms of Perfluorosulfonic Acid Mem‐

branes and Their Mitigation Strategies: A Review. Sustain. Energy Fuels 2017, 1, 409–438. https://doi.org/10.1039/C7SE00038C.

141. Bunlengsuwan, P.; Paradee, N.; Sirivat, A. Influence of Sulfonated Graphene Oxide on Sulfonated Polysulfone Membrane for

Direct Methanol Fuel Cell. Polym.‐Plast. Technol. Eng. 2017, 56, 1695–1703. https://doi.org/10.1080/03602559.2017.1289398.

142. Dutta, K.; Kumar, P.; Das, S.; Kundu, P.P. Utilization of Conducting Polymers in Fabricating Polymer Electrolyte Membranes

for Application in Direct Methanol Fuel Cells. Polym. Rev. 2014, 54, 1–32. https://doi.org/10.1080/15583724.2013.839566.

143. Rosli, N.A.H.; Loh, K.S.; Wong, W.Y.; Yunus, R.M.; Lee, T.K.; Ahmad, A.; Chong, S.T. Review of Chitosan‐Based Polymers as

Proton Exchange Membranes and Roles of Chitosan‐Supported Ionic Liquids. Int. J. Mol. Sci. 2020, 21, 632.

https://doi.org/10.3390/ijms21020632.

144. Aricò, A.S.; Stassi, A.; D’Urso, C.; Sebastián, D.; Baglio, V. Synthesis of Pd3Co1@Pt/C Core‐Shell Catalysts for Methanol‐Tolerant

Cathodes of Direct Methanol Fuel Cells. Chem.‐A Eur. J. 2014, 20, 10679–10684. https://doi.org/10.1002/chem.201402062.

145. Choi, B.; Nam, W.‐H.; Chung, D.Y.; Park, I.‐S.; Yoo, S.J.; Song, J.C.; Sung, Y.‐E. Enhanced Methanol Tolerance of Highly Pd Rich

Pd‐Pt Cathode Electrocatalysts in Direct Methanol Fuel Cells. Electrochim. Acta 2015, 164, 235–242.

https://doi.org/10.1016/j.electacta.2015.02.203.

146. Baglio, V.; Stassi, A.; Barbera, O.; Giacoppo, G.; Sebastian, D.; D’Urso, C.; Schuster, M.; Bauer, B.; Bonde, J.L.; Aricò, A.S. Direct

Methanol Fuel Cell Stack for Auxiliary Power Units Applications Based on Fumapem® F‐1850 Membrane. Int. J. Hydrog. Energy


147. Prapainainar, P.; Pattanapisutkun, N.; Prapainainar, C.; Kongkachuichay, P. Incorporating Graphene Oxide to Improve the

Performance of Nafion‐Mordenite Composite Membranes for a Direct Methanol Fuel Cell. Int. J. Hydrog. Energy 2019, 44, 362–

378. https://doi.org/10.1016/j.ijhydene.2018.08.008.

148. Liu, G.; Tsen, W.‐C.; Jang, S.‐C.; Hu, F.; Zhong, F.; Zhang, B.; Wang, J.; Liu, H.; Wang, G.; Wen, S.; et al. Composite Membranes

from Quaternized Chitosan Reinforced with Surface‐Functionalized PVDF Electrospun Nanofibers for Alkaline Direct Metha‐

nol Fuel Cells. J. Membr. Sci. 2020, 611, 118242. https://doi.org/10.1016/j.memsci.2020.118242.

149. Mollá, S.; Compañ, V. Polyvinyl Alcohol Nanofiber Reinforced Nafion Membranes for Fuel Cell Applications. J. Membr. Sci.

2011, 372, 191–200. https://doi.org/10.1016/j.memsci.2011.02.001.

150. Li, H.‐Y.; Lee, Y.‐Y.; Lai, J.‐Y.; Liu, Y.‐L. Composite Membranes of Nafion and Poly(Styrene Sulfonic Acid)‐Grafted Poly(Vinyl‐

idene Fluoride) Electrospun Nanofiber Mats for Fuel Cells. J. Membr. Sci. 2014, 466, 238–245. https://doi.org/10.1016/j.mem‐

sci.2014.04.057.

151. Xu, G.; Wu, Z.; Xie, Z.; Wei, Z.; Li, J.; Qu, K.; Li, Y.; Cai, W. Graphene Quantum Dot Reinforced Hyperbranched Polyamide

Proton Exchange Membrane for Direct Methanol Fuel Cell. Int. J. Hydrog. Energy 2021, 46, 9782–9789.


152. Zhang, X.; Zhang, M.; Deng, Y.; Xu, M.; Artiglia, L.; Wen, W.; Gao, R.; Chen, B.; Yao, S.; Zhang, X.; et al. A Stable Low‐Temper‐

ature H2‐Production Catalyst by Crowding Pt on α‐MoC. Nature 2021, 589, 396–401. https://doi.org/10.1038/s41586‐020‐03130‐

6.

153. Ramli, Z.A.C.; Kamarudin, S.K. Platinum‐Based Catalysts on Various Carbon Supports and Conducting Polymers for Direct

Methanol Fuel Cell Applications: A Review. Nanoscale Res. Lett. 2018, 13, 1–25. https://doi.org/10.1186/s11671‐018‐2799‐4.

154. Sahin, O.; Kivrak, H. A Comparative Study of Electrochemical Methods on Pt–Ru DMFC Anode Catalysts: The Effect of Ru

Addition. Int. J. Hydrog. Energy 2013, 38, 901–909. https://doi.org/10.1016/j.ijhydene.2012.10.066.

155. Nie, M.; Du, S.; Li, Q.; Hummel, M.; Gu, Z.; Lu, S. Tungsten Carbide as Supports for Trimetallic AuPdPt Electrocatalysts for

Methanol Oxidation. J. Electrochem. Soc. 2020, 167, 044510. https://doi.org/10.1149/1945‐7111/ab754d.

156. Bresciani, F.; Rabissi, C.; Casalegno, A.; Zago, M.; Marchesi, R. Experimental Investigation on DMFC Temporary Degradation.

Int. J. Hydrog. Energy 2014, 39, 21647–21656. https://doi.org/10.1016/j.ijhydene.2014.09.072.

157. Yaldagard, M.; Jahanshahi, M.; Seghatoleslami, N. Carbonaceous Nanostructured Support Materials for Low Temperature Fuel

Cell Electrocatalysts—A Review. World J. Nano Sci. Eng. 2013, 3, 33. https://doi.org/10.4236/wjnse.2013.34017.


158. Yang, Z.; Kim, C.; Hirata, S.; Fujigaya, T.; Nakashima, N. Facile Enhancement in CO‐Tolerance of a Polymer‐Coated Pt Electro‐

catalyst Supported on Carbon Black: Comparison between Vulcan and Ketjenblack. ACS Appl. Mater. Interfaces 2015, 7, 15885–

15891. https://doi.org/10.1021/acsami.5b03371.

159. Motsoeneng, R.G.; Modibedi, R.M.; Mathe, M.K.; Khotseng, L.E.; Ozoemena, K.I. The Synthesis of PdPt/Carbon Paper via Sur‐

face Limited Redox Replacement Reactions for Oxygen Reduction Reaction. Int. J. Hydrog. Energy 2015, 40, 16734–16744.


160. Xie, J.; Zhang, Q.; Gu, L.; Xu, S.; Wang, P.; Liu, J.; Ding, Y.; Yao, Y.F.; Nan, C.; Zhao, M.; et al. Ruthenium–Platinum Core–Shell

Nanocatalysts with Substantially Enhanced Activity and Durability towards Methanol Oxidation. Nano Energy 2016, 21, 247–

257. https://doi.org/10.1016/j.nanoen.2016.01.013.

161. Jovanovič, P.; Šelih, V.S.; Šala, M.; Hočevar, S.; Ruiz‐Zepeda, F.; Hodnik, N.; Bele, M.; Gaberšček, M. Potentiodynamic Dissolu‐

tion Study of PtRu/C Electrocatalyst in the Presence of Methanol. Electrochim. Acta 2016, 211, 851–859.

https://doi.org/10.1016/j.electacta.2016.06.109.

162. Kovtunenko, V.A.; Karpenko‐Jereb, L. Lifetime of Catalyst under Voltage Cycling in Polymer Electrolyte Fuel Cell Due to Plat‐

inum Oxidation and Dissolution. Technologies 2021, 9, 80. https://doi.org/10.3390/technologies9040080.

163. Han, M.; Zeng, J.; Xia, J.; Liao, S. Effect of Thermal Treatment on Structural Change of Anode Electrocatalysts for Direct Meth‐

anol Fuel Cells. Particuology 2014, 15, 45–50. https://doi.org/10.1016/j.partic.2012.12.007.

164. Sharma, R.; Gyergyek, S.; Lund, P.B.; Andersen, S.M. Recovery of Pt and Ru from Spent Low‐Temperature Polymer Electrolyte

Membrane Fuel Cell Electrodes and Recycling of Pt by Direct Redeposition of the Dissolved Precursor on Carbon. ACS Appl.

Energy Mater. 2021, 4, 6842–6852. https://doi.org/10.1021/acsaem.1c00964.

165. Zhang, C.; Yue, X.; Luan, J.; Lu, N.; Mu, Y.; Zhang, S.; Wang, G. Reinforced Poly(Ether Ether Ketone)/Nafion Composite Mem‐

brane with Highly Improved Proton Conductivity for High Concentration Direct Methanol Fuel Cells. ACS Appl. Energy Mater.

2020, 3, 7180–7190. https://doi.org/10.1021/acsaem.0c01212.

166. Schoekel, A.; Melke, J.; Bruns, M.; Wippermann, K.; Kuppler, F.; Roth, C. Quantitative Study of Ruthenium Cross‐over in Direct

Methanol Fuel Cells during Early Operation Hours. J. Power Sources 2016, 301, 210–218. https://doi.org/10.1016/j.jpow‐

sour.2015.09.119.

167. Lee, K.‐S.; Jeon, T.‐Y.; Yoo, S.J.; Park, I.‐S.; Cho, Y.‐H.; Kang, S.H.; Choi, K.H.; Sung, Y.‐E. Effect of PtRu Alloying Degree on

Electrocatalytic Activities and Stabilities. Appl. Catal. B: Environ. 2011, 102, 334–342. https://doi.org/10.1016/j.apcatb.2010.12.023.

168. Arlt, T.; Manke, I.; Wippermann, K.; Riesemeier, H.; Mergel, J.; Banhart, J. Investigation of the Local Catalyst Distribution in an

Aged Direct Methanol Fuel Cell MEA by Means of Differential Synchrotron X‐Ray Absorption Edge Imaging with High Energy

Resolution. J. Power Sources 2013, 221, 210–216. https://doi.org/10.1016/j.jpowsour.2012.08.038.

169. Sun, Y.; Zhou, Y.; Zhu, C.; Hu, L.; Han, M.; Wang, A.; Huang, H.; Liu, Y.; Kang, Z. A Pt–Co3O4–CD Electrocatalyst with En‐

hanced Electrocatalytic Performance and Resistance to CO Poisoning Achieved by Carbon Dots and Co3O4 for Direct Methanol

Fuel Cells. Nanoscale 2017, 9, 5467–5474. https://doi.org/10.1039/C7NR01727H.

170. Abdelkareem, M.A.; Masdar, M.S.; Tsujiguchi, T.; Nakagawa, N.; Sayed, E.T.; Barakat, N.A.M. Elimination of Toxic Products

Formation in Vapor‐Feed Passive DMFC Operated by Absolute Methanol Using Air Cathode Filter. Chem. Eng. J. 2014, 240, 38–

44. https://doi.org/10.1016/j.cej.2013.11.043.

171. Chung, D.Y.; Lee, K.‐J.; Sung, Y.‐E. Methanol Electro‐Oxidation on the Pt Surface: Revisiting the Cyclic Voltammetry Interpre‐

tation. J. Phys. Chem. C 2016, 120, 9028–9035. https://doi.org/10.1021/acs.jpcc.5b12303.

172. Park, S.‐H.; Joo, S.‐J.; Kim, H.‐S. An Investigation into Methanol Oxidation Reactions and CO, OH Adsorption on Pt‐Ru‐Mo

Catalysts for a Direct Methanol Fuel Cell. J. Electrochem. Soc. 2014, 161, F405. https://doi.org/10.1149/2.038404jes.

173. Siller‐Ceniceros, A.A.; Sánchez‐Castro, M.E.; Morales‐Acosta, D.; Torres‐Lubian, J.R.; Martínez, G.E.; Rodríguez‐Varela, F.J. In‐

novative Functionalization of Vulcan XC‐72 with Ru Organometallic Complex: Significant Enhancement in Catalytic Activity

of Pt/C Electrocatalyst for the Methanol Oxidation Reaction (MOR). Appl. Catal. B: Environ. 2017, 209, 455–467.

https://doi.org/10.1016/j.apcatb.2017.03.023.

174. Karuppanan, K.K.; Panthalingal, M.K.; Biji, P. Chapter 26—Nanoscale, Catalyst Support Materials for Proton‐Exchange Mem‐

brane Fuel Cells. In Handbook of Nanomaterials for Industrial Applications; Hussain, C.M., Ed.; Micro and Nano Technologies;

Elsevier: Amsterdam, The Netherlands, 2018; pp. 468–495, ISBN 978‐0‐12‐813351‐4.

175. Baruah, B.; Deb, P. Performance and Application of Carbon‐Based Electrocatalysts in Direct Methanol Fuel Cell. Mater. Adv.

2021, 2, 5344–5364. https://doi.org/10.1039/D1MA00503K.

176. Sundqvist, B. Carbon under Pressure. Phys. Rep. 2021, 909, 1–73. https://doi.org/10.1016/j.physrep.2020.12.007. 177. Zainoodin, A.M.; Kamarudin, S.K.; Masdar, M.S.; Daud, W.R.W.; Mohamad, A.B.; Sahari, J. Investigation of MEA Degradation

in a Passive Direct Methanol Fuel Cell under Different Modes of Operation. Appl. Energy 2014, 135, 364–372.

https://doi.org/10.1016/j.apenergy.2014.08.036.

178. Tsukagoshi, Y.; Ishitobi, H.; Nakagawa, N. Improved Performance of Direct Methanol Fuel Cells with the Porous Catalyst Layer

Using Highly‐Active Nanofiber Catalyst. Carbon Resour. Convers. 2018, 1, 61–72. https://doi.org/10.1016/j.crcon.2018.03.001.

179. Abdullah, N.; Kamarudin, S.K.; Shyuan, L.K. Novel Anodic Catalyst Support for Direct Methanol Fuel Cell: Characterizations

and Single‐Cell Performances. Nanoscale Res. Lett. 2018, 13, 1–13. https://doi.org/10.1186/s11671‐018‐2498‐1.

180. Vu, T.H.T.; Nguyen, M.D.; Mai, A.T.N. Influence of Solvents on the Electroactivity of PtAl/RGO Catalyst Inks and Anode in

Direct Ethanol Fuel Cell. J. Chem. 2021, 2021, e6649089. https://doi.org/10.1155/2021/6649089.


181. So, M.; Ohnishi, T.; Park, K.; Ono, M.; Tsuge, Y.; Inoue, G. The Effect of Solvent and Ionomer on Agglomeration in Fuel Cell

Catalyst Inks: Simulation by the Discrete Element Method. Int. J. Hydrog. Energy 2019, 44, 28984–28995.


182. Lashkenari, M.S.; Ghorbani, M.; Silakhori, N.; Karimi‐Maleh, H. Enhanced Electrochemical Performance and Stability of Pt/Ni

Electrocatalyst Supported on SiO2‐PANI Nanocomposite: A Combined Experimental and Theoretical Study. Mater. Chem. Phys.

2021, 262, 124290. https://doi.org/10.1016/j.matchemphys.2021.124290.

183. Robinson, J.E.; Labrador, N.Y.; Chen, H.; Sartor, B.E.; Esposito, D.V. Silicon Oxide‐Encapsulated Platinum Thin Films as Highly

Active Electrocatalysts for Carbon Monoxide and Methanol Oxidation. ACS Catal. 2018, 8, 11423–11434.

https://doi.org/10.1021/acscatal.8b03626.

184. Yusoff, N.; Kumar, S.V.; Rameshkumar, P.; Pandikumar, A.; Shahid, M.M.; Rahman, M.A.; Huang, N.M. A Facile Preparation

of Titanium Dioxide‐Iron Oxide@Silicon Dioxide Incorporated Reduced Graphene Oxide Nanohybrid for Electrooxidation of

Methanol in Alkaline Medium. Electrochim. Acta 2016, 192, 167–176. https://doi.org/10.1016/j.electacta.2016.01.190.

185. Mansor, M.; Timmiati, S.N.; Wong, W.Y.; Mohd Zainoodin, A.; Lim, K.L.; Kamarudin, S.K. NiPd Supported on Mesostructured

Silica Nanoparticle as Efficient Anode Electrocatalyst for Methanol Electrooxidation in Alkaline Media. Catalysts 2020, 10, 1235.

https://doi.org/10.3390/catal10111235.

186. Niyaz, M.; Sawut, N.; Jamal, R.; Abdiryim, T.; Helil, Z.; Liu, H.; Xie, S.; Song, Y. Preparation of PEDOT‐Modified Double‐Lay‐

ered Hollow Carbon Spheres as Pt Catalyst Support for Methanol Oxidation. Int. J. Hydrog. Energy 2021, 46, 31623–31633.


187. Yin, S.; Wang, Z.; Li, C.; Yu, H.; Deng, K.; Xu, Y.; Li, X.; Wang, L.; Wang, H. Mesoporous Pt@PtM (M = Co, Ni) Cage‐Bell

Nanostructures toward Methanol Electro‐Oxidation. Nanoscale Adv. 2020, 2, 1084–1089. https://doi.org/10.1039/D0NA00020E.

188. Jayakumar, A.; Sethu, S.P.; Ramos, M.; Robertson, J.; Al‐Jumaily, A. A Technical Review on Gas Diffusion, Mechanism and

Medium of PEM Fuel Cell. Ionics 2015, 21, 1–18. https://doi.org/10.1007/s11581‐014‐1322‐x.

189. Deng, H.; Zhang, Y.; Zheng, X.; Li, Y.; Zhang, X.; Liu, X. A CNT (Carbon Nanotube) Paper as Cathode Gas Diffusion Electrode

for Water Management of Passive μ‐DMFC (Micro‐Direct Methanol Fuel Cell) with Highly Concentrated Methanol. Energy

2015, 82, 236–241. https://doi.org/10.1016/j.energy.2015.01.034.

190. Chen, Y.; Ke, Y.; Xia, Y.; Cho, C. Investigation on Mechanical Properties of a Carbon Paper Gas Diffusion Layer through a 3‐D

Nonlinear and Orthotropic Constitutive Model. Energies 2021, 14, 6341. https://doi.org/10.3390/en14196341.

191. Randrianarizafy, B.; Schott, P.; Gerard, M.; Bultel, Y. Modelling Carbon Corrosion during a PEMFC Startup: Simulation of Mit‐

igation Strategies. Energies 2020, 13, 2338. https://doi.org/10.3390/en13092338.

192. Jayakumar, A. A Comprehensive Assessment on the Durability of Gas Diffusion Electrode Materials in PEM Fuel Cell Stack.

Front. Energy 2019, 13, 325–338. https://doi.org/10.1007/s11708‐019‐0618‐y.

193. Pethaiah, S.S.; Sadasivuni, K.K.; Jayakumar, A.; Ponnamma, D.; Tiwary, C.S.; Sasikumar, G. Methanol Electrolysis for Hydrogen

Production Using Polymer Electrolyte Membrane: A Mini‐Review. Energies 2020, 13, 5879. https://doi.org/10.3390/en13225879.

194. Kothekar, K.P.; Shrivastava, N.K.; Thombre, S.B. 11—Gas Diffusion Layers for Direct Methanol Fuel Cells. In Direct Methanol

Fuel Cell Technology; Dutta, K., Ed.; Elsevier: Amsterdam, The Netherlands, 2020; pp. 317–339, ISBN 978‐0‐12‐819158‐3.

195. Hsieh, S.‐S.; Chen, I.‐C.; Hwong, C.‐H. Development of a Four‐Cell DMFC Stack with Air‐Breathing Cathode and Dendrite Flow

Field. Int. J. Energy Res. 2014, 38, 1693–1711. https://doi.org/10.1002/er.3184.

196. Hwang, C.M.; Ishida, M.; Ito, H.; Maeda, T.; Nakano, A.; Hasegawa, Y.; Yokoi, N.; Kato, A.; Yoshida, T. Influence of Properties

of Gas Diffusion Layers on the Performance of Polymer Electrolyte‐Based Unitized Reversible Fuel Cells. Int. J. Hydrog. Energy


197. Liu, G.; Li, X.; Wang, H.; Liu, X.; Chen, M.; Woo, J.Y.; Kim, J.Y.; Wang, X.; Lee, J.K. Design of 3‐Electrode System for in Situ

Monitoring Direct Methanol Fuel Cells during Long‐Time Running Test at High Temperature. Appl. Energy 2017, 197, 163–168.


198. García‐Salaberri, P.A.; Vera, M. On the Effect of Operating Conditions in Liquid‐Feed Direct Methanol Fuel Cells: A Multiphys‐

ics Modeling Approach. Energy 2016, 113, 1265–1287. https://doi.org/10.1016/j.energy.2016.07.074.

199. Kim, Y.‐S.; Peck, D.‐H.; Kim, S.‐K.; Jung, D.‐H.; Lim, S.; Kim, S.‐H. Effects of the Microstructure and Powder Compositions of a

Micro‐Porous Layer for the Anode on the Performance of High Concentration Methanol Fuel Cell. Int. J. Hydrog. Energy 2013,

38, 7159–7168. https://doi.org/10.1016/j.ijhydene.2013.04.003.

200. He, Y.‐L.; Miao, Z.; Zhao, T.‐S.; Yang, W.‐W. Numerical Study of the Effect of the GDL Structure on Water Crossover in a Direct

Methanol Fuel Cell. Int. J. Hydrog. Energy 2012, 37, 4422–4438. https://doi.org/10.1016/j.ijhydene.2011.11.102.

201. Lee, K.; Ferekh, S.; Jo, A.; Lee, S.; Ju, H. Effects of Hybrid Catalyst Layer Design on Methanol and Water Transport in a Direct

Methanol Fuel Cell. Electrochim. Acta 2015, 177, 209–216. https://doi.org/10.1016/j.electacta.2015.02.222.

202. Yuan, W.; Zhang, X.; Hou, C.; Zhang, Y.; Wang, H.; Liu, X. Enhanced Water Management via the Optimization of Cathode

Microporous Layer Using 3D Graphene Frameworks for Direct Methanol Fuel Cell. J. Power Sources 2020, 451, 227800.

https://doi.org/10.1016/j.jpowsour.2020.227800.

203. Deng, H.; Zhou, J.; Zhang, Y. A Trilaminar‐Catalytic Layered MEA Structure for a Passive Micro‐Direct Methanol Fuel Cell.

Micromachines 2021, 12, 381. https://doi.org/10.3390/mi12040381.

204. Ko, J.; Kang, K.; Park, S.; Kim, W.‐G.; Lee, S.‐H.; Ju, H. Effect of Design of Multilayer Electrodes in Direct Methanol Fuel Cells

(DMFCs). Int. J. Hydrog. Energy 2014, 39, 1571–1579. https://doi.org/10.1016/j.ijhydene.2013.04.069.


205. Yuan, W.; Han, F.; Chen, Y.; Chen, W.; Hu, J.; Tang, Y. Enhanced Water Management and Fuel Efficiency of a Fully Passive

Direct Methanol Fuel Cell with Super‐Hydrophilic/ ‐Hydrophobic Cathode Porous Flow‐Field. J. Electrochem. Energy Convers.

Storage 2018, 15, 031003. https://doi.org/10.1115/1.4039298.

206. Chan, D.‐S.; Hsueh, K.‐L. A Transient Model for Fuel Cell Cathode‐Water Propagation Behavior inside a Cathode after a Step

Potential. Energies 2010, 3, 920–939. https://doi.org/10.3390/en3050920.

207. Wu, Q.X.; Zhao, T.S.; Yang, W.W. Effect of the Cathode Gas Diffusion Layer on the Water Transport Behavior and the Perfor‐

mance of Passive Direct Methanol Fuel Cells Operating with Neat Methanol. Int. J. Heat Mass Transf. 2011, 54, 1132–1143.

https://doi.org/10.1016/j.ijheatmasstransfer.2010.11.009.

208. Shrestha, S. Fuel Cell : Direct Methanol Fuel Cell (DMFC). Available online: https://energyandclimatechangeinfo.blog‐

spot.com/2021/06/direct‐methanol‐fuel‐cell‐dmfc‐uses.html (accessed on 12 February 2021).

209. Kim, J.H.; Lee, G.G.; Kim, W.T. Comparison of Liquid Water Dynamics in Bent Gas Channels of a Polymer Electrolyte Mem‐

brane Fuel Cell with Different Channel Cross Sections in a Channel Flooding Situation. Energies 2017, 10, 748.

https://doi.org/10.3390/en10060748.

210. Li, X.; Faghri, A.; Xu, C. Water Management of the DMFC Passively Fed with a High‐Concentration Methanol Solution. Int. J.


211. Wang, Z.; Zhang, X.; Nie, L.; Zhang, Y.; Liu, X. Elimination of Water Flooding of Cathode Current Collector of Micro Passive

Direct Methanol Fuel Cell by Superhydrophilic Surface Treatment. Appl. Energy 2014, 126, 107–112.


212. Sun, J.; Zhang, G.; Guo, T.; Che, G.; Jiao, K.; Huang, X. Effect of Anisotropy in Cathode Diffusion Layers on Direct Methanol

Fuel Cell. Appl. Therm. Eng. 2020, 165, 114589. https://doi.org/10.1016/j.applthermaleng.2019.114589.

213. Zhang, J.; Feng, L.; Cai, W.; Liu, C.; Xing, W. The Function of Hydrophobic Cathodic Backing Layers for High Energy Passive

Direct Methanol Fuel Cell. J. Power Sources 2011, 196, 9510–9515. https://doi.org/10.1016/j.jpowsour.2011.07.039.

214. Fu, X.; Ni, H.; Zhang, F.; Yang, Y.; Shao, X.; Huang, Z.; Zhang, R.; Liu, Q.; Hu, S. Polypyrrole Nanowires as a Cathode Mi‐

croporous Layer for Direct Methanol Fuel Cell to Enhance Oxygen Transport. Int. J. Energy Res. 2021, 45, 3375–3384.

https://doi.org/10.1002/er.5976.

215. Hutzenlaub, T.; Paust, N.; Zengerle, R.; Ziegler, C. The Effect of Wetting Properties on the Bubble Dynamics in the Flow Field

of Direct Methanol Fuel Cells. Meet. Abstr. 2010, 3, 177. https://doi.org/10.1149/MA2010‐01/3/177.

216. Yuan, W.; Hou, C.; Zhang, X.; Zhong, S.; Luo, Z.; Mo, D.; Zhang, Y.; Liu, X. Constructing a Cathode Catalyst Layer of a Passive

Direct Methanol Fuel Cell with Highly Hydrophilic Carbon Aerogel for Improved Water Management. ACS Appl. Mater. Inter‐

faces 2019, 11, 37626–37634. https://doi.org/10.1021/acsami.9b09713.

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